<PAGE>   1
 
   AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON SEPTEMBER 29, 1999
                                                      REGISTRATION NO. 333-
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
 
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                            ------------------------
 
                                    FORM S-1
                             REGISTRATION STATEMENT
                                     UNDER
                           THE SECURITIES ACT OF 1933
                            ------------------------
 
                     INTERNAP NETWORK SERVICES CORPORATION
             (EXACT NAME OF REGISTRANT AS SPECIFIED IN ITS CHARTER)
 

<TABLE>
<S>                                  <C>                                  <C>
             WASHINGTON                              7374                              91-1896926
  (STATE OR OTHER JURISDICTION OF        (PRIMARY STANDARD INDUSTRIAL               (I.R.S. EMPLOYER
   INCORPORATION OR ORGANIZATION)        CLASSIFICATION CODE NUMBER)             IDENTIFICATION NUMBER)
</TABLE>

 
                          601 UNION STREET, SUITE 1000
                           SEATTLE, WASHINGTON 98101
                                 (206) 441-8800
  (ADDRESS, INCLUDING ZIP CODE, AND TELEPHONE NUMBER, INCLUDING AREA CODE, OF
                   REGISTRANT'S PRINCIPAL EXECUTIVE OFFICES)
 
                              ANTHONY C. NAUGHTIN
                     PRESIDENT AND CHIEF EXECUTIVE OFFICER
                     INTERNAP NETWORK SERVICES CORPORATION
                          601 UNION STREET, SUITE 1000
                           SEATTLE, WASHINGTON 98101
                                 (206) 441-8800
 (NAME, ADDRESS, INCLUDING ZIP CODE, AND TELEPHONE NUMBER, INCLUDING AREA CODE,
                             OF AGENT FOR SERVICE)
 
                                   COPIES TO:
 

<TABLE>
<S>                                                    <C>
             CHRISTOPHER W. WRIGHT, ESQ.                            PETER E. WILLIAMS III, ESQ.
               DOUGLAS H. HAEUBER, ESQ.                                 VICTOR H. SIM, ESQ.
                H. MARLOW GREEN, ESQ.                                  MAILE Y.C. YANG, ESQ.
                  COOLEY GODWARD LLP                                  MORRISON & FOERSTER LLP
                 5200 CARILLON POINT                                     755 PAGE MILL ROAD
               KIRKLAND, WA 98033-7355                                PALO ALTO, CA 94304-1018
                    (425) 893-7700                                         (650) 813-5652
</TABLE>

 
        APPROXIMATE DATE OF COMMENCEMENT OF PROPOSED SALE TO THE PUBLIC:
   As soon as practicable after the Registration Statement becomes effective.
 
    If any of the securities being registered on this Form are to be offered on
a delayed or continuous basis pursuant to Rule 415 under the Securities Act,
check the following box.  [ ]
 
    If this Form is filed to register additional securities for an offering
pursuant to Rule 462(b) under the Securities Act, check the following box and
list the Securities Act registration statement number of the earlier effective
registration statement for the same offering.  [X]  333-84035
 
    If this Form is a post-effective amendment filed pursuant to Rule 462(c)
under the Securities Act, check the following box and list the Securities Act
registration statement number of the earlier effective registration statement
number for the same offering.  [ ]
---------------
 
    If this Form is a post-effective amendment filed pursuant to Rule 462(d)
under the Securities Act, check the following box and list the Securities Act
registration number of the earlier effective registration statement for the same
offering.  [ ]
---------------
 
    If delivery of the prospectus is expected to be made pursuant to Rule 434,
please check the following box.  [ ]
 
                        CALCULATION OF REGISTRATION FEE
 

<TABLE>
<S>                                      <C>                  <C>                  <C>                  <C>
---------------------------------------------------------------------------------------------------------------------------
---------------------------------------------------------------------------------------------------------------------------
                                                               PROPOSED MAXIMUM     PROPOSED MAXIMUM
   TITLE OF EACH CLASS OF SECURITIES        AMOUNT TO BE      OFFERING PRICE PER   AGGREGATE OFFERING        AMOUNT OF
           TO BE REGISTERED               REGISTERED(1)(2)         SHARE(3)             PRICE(3)         REGISTRATION FEE
---------------------------------------------------------------------------------------------------------------------------
Common Stock, $.001 par value per
  share................................        920,000              $20.00             $18,400,000           $5,116(4)
---------------------------------------------------------------------------------------------------------------------------
---------------------------------------------------------------------------------------------------------------------------
</TABLE>

 
(1) Includes 120,000 shares which the underwriters have the option to purchase
    to cover over-allotments, if any.
 
(2) Does not include 10,005,000 shares of Common Stock previously registered for
    which the registration fee has previously been paid.
 
(3) The proposed maximum offering price per share and the proposed maximum
    aggregate offering price are based on the proposed offering price for the
    shares of Common Stock offered hereby.
 
(4) Calculated pursuant to Rule 457(a).
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------

<PAGE>   2
 
               INCORPORATION OF CERTAIN INFORMATION BY REFERENCE
 
     This Registration Statement filed under the Securities Act of 1933, as
amended, by InterNAP Network Services Corporation (the "Company") with the
Securities and Exchange Commission (the "Commission") hereby incorporates by
reference the contents of the Registration Statement on Form S-1, as amended,
(File No. 333-84035) relating to the offering of up to 10,005,000 shares of
Common Stock of the Company initially filed on July 29, 1999.
 
                                 CERTIFICATION
 
     The Company hereby certifies to the Commission that it has instructed its
bank to pay the Commission the filing fee of $5,116 for the additional
securities being registered hereby as soon as practicable (but in any event no
later than the close of business on September 29, 1999); that it will not revoke
such instructions; that it has sufficient funds in the relevant account to cover
the amount of the filing fee; and that it undertakes to confirm receipt of such
instructions by the bank on September 29, 1999.
 
                                        1

<PAGE>   3
 
                                   SIGNATURES
 
     Pursuant to the requirements of the Securities Act of 1933, as amended, the
Company has duly caused this Registration Statement to be signed on its behalf
by the undersigned, thereinto duly authorized, in the City of Seattle, State of
Washington, on the 29th day of September, 1999.
 
                                       INTERNAP NETWORK SERVICES
                                       CORPORATION
 
                                       By:                   *
                                         ---------------------------------------
                                                   Anthony C. Naughtin
                                          Chief Executive Officer and President
 
     Pursuant to the requirements of the Securities Act of 1933, as amended,
this Registration Statement has been signed by the following persons in the
capacities and on the dates indicated:
 

<TABLE>
<CAPTION>
                      SIGNATURE                                    TITLE                      DATE
                      ---------                                    -----                      ----
<S>                                                    <C>                             <C>
                          *                             Chief Executive Officer and    September 29, 1999
-----------------------------------------------------  President (Principal Executive
                 Anthony C. Naughtin                              Officer)
 
                 /s/ PAUL E. MCBRIDE                      Vice President and Chief     September 29, 1999
-----------------------------------------------------   Financial Officer (Principal
                   Paul E. McBride                         Finance and Accounting
                                                                  Officer)
 
                          *                                Chairman of the Board       September 29, 1999
-----------------------------------------------------
                  Eugene Eidenberg
 
                          *                                       Director             September 29, 1999
-----------------------------------------------------
                 William J. Harding
 
                          *                                       Director             September 29, 1999
-----------------------------------------------------
                 Frederic W. Harman
 
                          *                                       Director             September 29, 1999
-----------------------------------------------------
                Robert J. Lunday, Jr.
 
                          *                                       Director             September 29, 1999
-----------------------------------------------------
                    Kevin L. Ober
 
                          *                                       Director             September 29, 1999
-----------------------------------------------------
              Robert D. Shurtleff, Jr.
 
               By: /s/ PAUL E. MCBRIDE
  -------------------------------------------------
                   Paul E. McBride
                 (Attorney-in-Fact)
</TABLE>

 
                                        2

<PAGE>   4
 
                                 EXHIBIT INDEX
 

<TABLE>
<CAPTION>
EXHIBIT
NUMBER                            DESCRIPTION
-------                           -----------
<C>       <S>
  5.1     Opinion of Cooley Godward LLP.
 23.1     Consent of Counsel (included in Exhibit 5.1).
 23.2     Consent of PricewaterhouseCoopers LLP, Independent
          Accountants.
 24.1+    Power of Attorney.
 27.1     Financial Data Schedule.
</TABLE>

 
---------------
+ Incorporated by reference to the Signature Page of the Company's Registration
  Statement on Form S-1 (File No. 333-84035) initially filed on July 29, 1999.





<PAGE>   1

                                                                     EXHIBIT 5.1

                        [COOLEY GODWARD LLP LETTERHEAD]

September 29, 1999

InterNAP Network Services Corporation
601 Union Street, Suite 1000
Seattle, WA 98101

Ladies and Gentlemen:

You have requested our opinion with respect to certain matters in connection
with the filing by InterNAP Network Services Corporation (the "Company") of a
Registration Statement on Form S-1 (the "Registration Statement") with the
Securities and Exchange Commission (the "Commission") covering an underwritten
public offering of up to ten million nine hundred twenty five thousand
(10,925,000) shares of Common Stock (the "Common Stock").

In connection with this opinion, we have (i) examined and relied upon the
Registration Statement and related Prospectus, the Company's Articles of
Incorporation,as amended, and Bylaws, as currently in effect, and the originals
or copies certified to our satisfaction of such records, documents,
certificates, memoranda and other instruments as in our judgment are necessary
or appropriate to enable us to render the opinion expressed below; (ii) assumed
that the Amended and Restated Articles of Incorporation, as set forth in Exhibit
3.2 of the Registration Statement, shall have been duly approved and filed with

the office of the Washington Secretary of State; and (iii) that the shares of
Common Stock will be sold by the Underwriters at a price established by the
Pricing Committee of the Board of Directors of the Company.

On the basis of the foregoing, and in reliance thereon, we are of the opinion
that the Common Stock, when sold and issued in accordance with the Registration
Statement and related Prospectus, will be validly issued, fully paid and
non-assessable.

We consent to the reference to our firm under the caption "Legal Matters"
in the Prospectus included in the Registration Statement and to the filing of
this opinion as an exhibit to the Registration Statement.

Very truly yours,

COOLEY GODWARD LLP

By:  /s/ CHRISTOPHER W. WRIGHT
     ------------------------------
     Christopher W. Wright



<PAGE>   1
                                                                    EXHIBIT 23.1


                       CONSENT OF INDEPENDENT ACCOUNTANTS


We hereby consent to the use of our reports dated April 2, 1999 relating to the
financial statements and financial statement schedule of InterNAP Network
Services Corporation in this Registration Statement on Form S-1 for the
registration of 920,000 shares of common stock, which incorporates by reference
the Registration Statement on Form S-1 (No. 333-84035) and the related
prospectus of InterNAP Network Services Corporation declared effective September
29, 1999. We also consent to the reference to us under the headings "Experts"
and "Selected Financial Data" in such Registration Statement.



PricewaterhouseCoopers LLP


Seattle, Washington
September 27, 1999





<TABLE> <S> <C>

<ARTICLE> 5
<MULTIPLIER> 1000
       
<S>                             <C>
<PERIOD-TYPE>                   6-MOS
<FISCAL-YEAR-END>                          DEC-31-1999
<PERIOD-START>                             JAN-01-1999
<PERIOD-END>                               JUN-30-1999
<CASH>                                           3,301
<SECURITIES>                                     9,995
<RECEIVABLES>                                    1,655
<ALLOWANCES>                                        78
<INVENTORY>                                          0
<CURRENT-ASSETS>                                15,070
<PP&E>                                          15,975
<DEPRECIATION>                                   2,310
<TOTAL-ASSETS>                                  30,830
<CURRENT-LIABILITIES>                            6,780
<BONDS>                                          6,776
<PREFERRED-MANDATORY>                                0
<PREFERRED>                                         50
<COMMON>                                             4
<OTHER-SE>                                      17,220
<TOTAL-LIABILITY-AND-EQUITY>                    30,830
<SALES>                                          3,410
<TOTAL-REVENUES>                                 3,410
<CGS>                                                0
<TOTAL-COSTS>                                   19,862
<OTHER-EXPENSES>                                 (303)
<LOSS-PROVISION>                                    58
<INTEREST-EXPENSE>                                 147
<INCOME-PRETAX>                               (16,149)
<INCOME-TAX>                                         0
<INCOME-CONTINUING>                                  0
<DISCONTINUED>                                       0
<EXTRAORDINARY>                                      0
<CHANGES>                                            0
<NET-INCOME>                                  (16,149)
<EPS-BASIC>                                     (4.78)
<EPS-DILUTED>                                   (4.78)
        

</TABLE>