<PAGE>
 
                                                                     EXHIBIT 4.2

          THIS NOTE (OR ITS PREDECESSOR) HAS NOT BEEN REGISTERED UNDER THE U.S.
SECURITIES ACT OF 1933, AS AMENDED (THE "SECURITIES ACT"), AND, ACCORDINGLY, MAY
NOT BE OFFERED, SOLD, PLEDGED OR OTHERWISE TRANSFERRED WITHIN THE UNITED STATES
OR TO, OR FOR THE ACCOUNT OR BENEFIT OF, U.S. PERSONS, EXCEPT AS SET FORTH IN
THE NEXT SENTENCE.   BY ITS ACQUISITION HEREOF OR OF A BENEFICIAL INTEREST
HEREIN, THE HOLDER:

          (1) REPRESENTS THAT (A) IT IS A "QUALIFIED INSTITUTIONAL BUYER" (AS
     DEFINED IN RULE 144A UNDER THE SECURITIES ACT) (A "QIB") OR (B) IT HAS
     ACQUIRED THIS NOTE IN AN OFFSHORE TRANSACTION IN COMPLIANCE WITH REGULATION
     S UNDER THE SECURITIES ACT,

          (2) AGREES THAT IT WILL NOT RESELL OR OTHERWISE TRANSFER THIS NOTE
     EXCEPT (A) TO THE COMPANY OR ANY OF ITS SUBSIDIARIES, (B) TO A PERSON WHOM
     THE SELLER REASONABLY BELIEVES IS A QIB PURCHASING FOR ITS OWN ACCOUNT OR
     FOR THE ACCOUNT OF A QIB IN A TRANSACTION MEETING THE REQUIREMENTS OF RULE
     144A, (C) IN AN OFFSHORE TRANSACTION MEETING THE REQUIREMENTS OF RULE 903
     OR 904 OF THE SECURITIES ACT, (D) IN A TRANSACTION MEETING THE REQUIREMENTS
     OF RULE 144 UNDER THE SECURITIES ACT, (E) IN ACCORDANCE WITH ANOTHER
     EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT (AND
     BASED UPON AN OPINION OF COUNSEL ACCEPTABLE TO THE COMPANY) OR (F) PURSUANT
     TO AN EFFECTIVE REGISTRATION STATEMENT AND, IN EACH CASE, IN ACCORDANCE
     WITH THE APPLICABLE SECURITIES LAWS OF ANY STATE OF THE UNITED STATES OR
     ANY OTHER APPLICABLE JURISDICTION AND
 
          (3) AGREES THAT IT WILL DELIVER TO EACH PERSON TO WHOM THIS NOTE OR AN
     INTEREST HEREIN IS TRANSFERRED A NOTICE SUBSTANTIALLY TO THE EFFECT OF THIS
     LEGEND.
 
          AS USED HEREIN, THE TERMS "OFFSHORE TRANSACTION" AND "UNITED STATES"
HAVE THE MEANINGS GIVEN TO THEM BY RULE 902 OF REGULATION S UNDER THE SECURITIES
ACT.  THE INDENTURE CONTAINS A PROVISION REQUIRING THE TRUSTEE TO REFUSE TO
REGISTER ANY TRANSFER OF THIS NOTE IN VIOLATION OF THE FOREGOING.

          THIS NOTE IS A GLOBAL NOTE WITHIN THE MEANING OF THE INDENTURE
HEREINAFTER REFERRED TO AND IS REGISTERED IN THE 
<PAGE>
 
NAME OF A DEPOSITARY OR A NOMINEE OF A DEPOSITARY OR A SUCCESSOR DEPOSITARY.
TRANSFERS OF THIS GLOBAL NOTE SHALL BE LIMITED TO TRANSFERS IN WHOLE, BUT NOT IN
PART, TO NOMINEES OF CEDE & CO. OR TO A SUCCESSOR THEREOF OR SUCH SUCCESSOR'S
NOMINEE AND TRANSFERS OF PORTIONS OF THIS GLOBAL NOTE SHALL BE LIMITED TO
TRANSFERS MADE IN ACCORDANCE WITH THE RESTRICTIONS SET FORTH IN SECTIONS 3.06
AND 3.07 OF THE INDENTURE.

          UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE
OF THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION ("DTC"), TO THE COMPANY
OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE, OR PAYMENT AND ANY SUCH
CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR IN SUCH OTHER NAME
AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC (AND ANY PAYMENT IS MADE
TO CEDE & CO. OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED
REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE, OR OTHER USE HEREOF FOR VALUE OR
OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE REGISTERED OWNER
HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.
<PAGE>
 
                                  PSINET INC.


                              ___________________


                     11 1/2% SENIOR NOTE DUE 2008, SERIES A

                             CUSIP NO. ____________

                       No. __             $______________


          PSINet Inc., a New York corporation (herein called the "Company",
which term includes any successor Person under the Indenture hereinafter
referred to), for value received, hereby promises to pay to _____________ or
registered assigns, the principal sum of ____________________________ United
States dollars on November 1, 2008, at the office or agency of the Company
referred to below, and to pay interest thereon from November 3, 1998, or from
the most recent Interest Payment Date to which interest has been paid or duly
provided for, semiannually on May 1 and November 1, in each year, commencing May
1, 1999 at the rate of 11 1/2% per annum, subject to adjustments as described in
the second following paragraph, in United States dollars, until the principal
hereof is paid or duly provided for.  Interest shall be computed on the basis of
a 360-day year comprised of twelve 30-day months.

          The Holder of this Series A Note is entitled to the benefits of either
the Registration Rights Agreement between the Company and the Initial
Purchasers, dated as of November 3, 1998, or the Registration Rights Agreement
between the Company and the Initial Purchasers, dated as of November 13, 1998,
pursuant to which, subject to the terms and conditions thereof, the Company is
obligated to consummate the Exchange Offer pursuant to which the Holder of this
Note shall have the right to exchange this Note for 11 1/2% Senior Notes due
2008, Series B (herein called the "Series B Notes") in like principal amount as
provided therein.  The Series A Notes and the Series B Notes are together
referred to as the "Notes".  The Series A Notes rank pari passu in right of
payment with the Series B Notes.

          In the event that (a) the Exchange Offer Registration Statement is not
filed with the Commission on or prior to the date specified in the Registration
Rights Agreement, (b) the Exchange Offer Registration Statement is not declared
effective on or prior to the date specified in the Registration Rights
Agreement, (c) the Exchange Offer is not consummated on or prior to the date
specified in the Registration Rights Agreement,
<PAGE>
 
(d) if obligated to file the Shelf Registration Statement, the Company fails to
file the Shelf Registration Statement with the Commission on or prior to the
date specified in the Registration Rights Agreement, (e) if obligated to file
the Shelf Registration Statement, the Shelf Registration Statement is not
declared effective on or prior to the date specified in the Registration Rights
Agreement, or (f) the Shelf Registration Statement or the Exchange Offer
Registration Statement is declared effective but thereafter ceases to be
effective or usable in connection with resales of the Series A Notes during the
periods specified in the Registration Rights Agreement (each such event referred
to in clauses (a) through (f) above, a "Registration Default"), the Company
agrees to pay to each Holder of Series A Notes liquidated damages ("Liquidated
Damages") in an amount equal to $0.05 per week per $1,000 in principal amount of
Series A Notes held by such Holder for each week or portion thereof that the
Registration Default continues for the first 90 day period immediately following
the occurrence of such Registration Default. The amount of Liquidated Damages
shall increase by an additional $0.05 per week per $1,000 in principal amount of
Series A Notes with respect to each subsequent 90 day period until all
Registration Defaults have been cured, up to a maximum amount of Liquidated
Damages of $0.50 per week per $1,000 in principal amount of Series A Notes. The
Company shall not be required to pay Liquidated Damages for more than one
Registration Default at any given time. Following the cure of all Registration
Defaults, the accrual of Liquidated Damages shall cease. All accrued Liquidated
Damages shall be paid by the Company to holders entitled thereto by wire
transfer to the accounts specified by them or by mailing checks to their
registered address if no such accounts have been specified.

          The interest so payable, and punctually paid or duly provided for, on
any Interest Payment Date will, as provided in the Indenture hereinafter
referred to, be paid to the Person in whose name this Note (or any Predecessor
Notes) is registered at the close of business on the Regular Record Date for
such interest, which shall be the April 15 or October 15 (whether or not a
Business Day), as the case may be, next preceding such Interest Payment Date.
Any such interest not so punctually paid, or duly provided for, and interest on
such defaulted interest at the interest rate borne by the Series A Notes, to the
extent lawful, shall forthwith cease to be payable to the Holder on such Regular
Record Date, and may either be paid to the Person in whose name this Note (or
any Predecessor Notes) is registered at the close of business on a Special
Record Date for the payment of such defaulted interest to be fixed by the
Trustee, notice whereof shall be given to Holders of Notes not less than 10 days
prior to such Special Record Date, or be paid at any time in any other lawful
manner not inconsistent with the requirements of any securities exchange on
which the Notes may be listed, and upon such notice as may be required by this
Indenture not inconsistent with the requirements of such exchange, all as more
fully provided in this Indenture.
<PAGE>
 
          Payment of the principal of, premium, if any, and interest on, this
Note, and exchange or transfer of the Note, will be made at the office or agency
of the Company in the City of New York maintained for that purpose (which
initially will be the Trustee c/o Harris  Trust Company of New York, 77 Water
Street, New York, NY 10005), or at such other office or agency as may be
maintained for such purpose, or, at the option of the Company, payment of
interest may be made by check mailed to the address of the Person entitled
thereto as such address shall appear on the Note Register, and provided, that
payment by wire transfer of immediately available funds will be required with
respect to principal of and interest on all Global Notes and all other Notes the
Holders of which shall have provided wire transfer instructions to the Company
or the Paying Agent.  Such payment shall be in such coin or currency of the
United States of America as at the time of payment is legal tender for payment
of public and private debts.

          Reference is hereby made to the further provisions of this Note set
forth on the reverse hereof, which further provisions shall for all purposes
have the same effect as if set forth at this place.

          Unless the certificate of authentication hereon has been duly executed
by the Trustee referred to on the reverse hereof or by the authenticating agent
appointed as provided in the Indenture by manual signature of an authorized
signer, this Note shall not be entitled to any benefit under the Indenture, or
be valid or obligatory for any purpose.
<PAGE>
 
          IN WITNESS WHEREOF, the Company has caused this instrument to be duly
executed by the manual or facsimile signature of its authorized officers and its
corporate seal to be affixed or reproduced hereon.

                         PSINET INC.


[Seal]                   By:___________________________
                         Title:________________________

Attest:


____________________________
Authorized Officer


                    TRUSTEE'S CERTIFICATE OF AUTHENTICATION


          This is one of the 11 1/2% Senior Notes due 2008, Series A referred to
in the within-mentioned Indenture.

                            WILMINGTON TRUST COMPANY,
                                as Trustee



                         By:  _________________________________
                                  Authorized Signer

Dated:

<PAGE>
 
                       OPTION OF HOLDER TO ELECT PURCHASE



          If you wish to have this Note purchased by the Company pursuant to
Section 10.12 or Section 10.14, as applicable, of the Indenture, check the Box:
[_].

          If you wish to have a portion of this Note purchased by the Company
pursuant to Section 10.12 or Section 10.14 as applicable, of the Indenture,
state the amount (in original principal amount):

               $ _______________.


Date:  ___________________


                              Your Signature:  _____________________


(Sign exactly as your name appears on the other side of this Note)


Signature Guarantee:  __________________________________


[Signature must be guaranteed by an eligible Guarantor Institution (banks, stock
brokers, savings and loan associations and credit unions) with membership in an
approved guarantee medallion program pursuant to Securities and Exchange
Commission Rule 17Ad-15]
<PAGE>
 
                                 (Back of Note)

                                  PSINET INC.
                     11 1/2% Senior Note due 2008, Series A

          This Note is one of a duly authorized issue of Notes of the Company
designated as its 11 1/2% Senior Notes due 2008, Series A (herein called the
"Notes"), limited (except as otherwise provided in the Indenture referred to
below) in aggregate principal amount to $350,000,000, issued under, entitled to
the benefits of  and subject to the terms of an indenture (herein called the
"Indenture") dated as of November 3, 1998, as amended, between the Company and
Wilmington Trust Company, as trustee (herein called the "Trustee," which term
includes any successor trustee under the Indenture), to which Indenture and all
indentures supplemental thereto reference is hereby made for a statement of the
respective rights, limitations of rights, duties, obligations and immunities
thereunder of the Company, any Guarantors, the Trustee and the Holders of the
Notes, and of the terms upon which the Notes are, and are to be, authenticated
and delivered.

          The Indenture contains provisions for defeasance at any time of (a)
the entire Indebtedness on the Notes and (b) certain restrictive covenants and
related Defaults and Events of Default, in each case upon compliance with
certain conditions set forth therein.

          The Notes are subject to redemption at any time on or after November
1, 2003, at the option of the Company, in whole or in part, on not less than 30
nor more than 60 days' prior notice, in amounts of $1,000 or an integral
multiple thereof, at the following redemption prices (expressed as percentages
of the principal amount), if redeemed during the 12-month period beginning
November 1 of the years indicated below:
<TABLE>
<CAPTION>
 
                                 Redemption
                          Year        Price
                          ----   ----------
                          <S>       <C>
                          2003    105.750%
                          2004    103.833%
                          2005    101.917%
                          2006    100.000%
</TABLE>

and thereafter at 100% of the principal amount, in each case, together with
accrued and unpaid interest, if any, to the Redemption Date (subject to the
rights of Holders of record on relevant record dates to receive interest due on
an Interest Payment Date).
<PAGE>
 
         In addition, at any time on or prior to November 1, 2001, the Company
may, at its option, use the net proceeds of one or more Public Equity Offerings
or the sale of Capital Stock (other than Disqualified Stock) of the Company to a
Strategic Investor in a single transaction or in a series of related
transactions, to redeem up to an aggregate of 35% of the aggregate principal
amount of Notes originally issued under the Indenture at a redemption price
equal to 111.5% of the aggregate principal amount thereof, plus accrued and
unpaid interest thereon, if any, to the Redemption Date; provided that at least
65% aggregate principal amount of Notes remains outstanding immediately after
the occurrence of such redemption.  In order to effect the foregoing redemption,
the Company must mail a notice of redemption no later than 45 days after the
closing of the related Public Equity Offering or to a Strategic Investor and
must consummate such redemption within 60 days of the closing of the Public
Equity Offering or sale to a Strategic Investor.

         If less than all of the Notes are to be redeemed, the Trustee shall
select the Notes or portions thereof to be redeemed pro rata, by lot or by any
other method the Trustee shall deem fair and reasonable.

         Upon the occurrence of a Change of Control, subject to the terms of the
Indenture, each Holder may require the Company to purchase such Holder's Notes
in whole or in part in integral multiples of $1,000, at a purchase price in cash
in an amount equal to 101% of the principal amount thereof, plus accrued and
unpaid interest, if any, to the date of purchase, pursuant to a Change of
Control Offer in accordance with the procedures set forth in the Indenture.

         Under certain circumstances, subject to the terms of the Indenture, in
the event the Net Cash Proceeds received by the Company from any Asset Sale,
which proceeds are not used to repay any Pari Passu Indebtedness of the Company
or any Subsidiary (including the repurchase of Notes) or which will be invested
in Telecommunications Assets, exceeds a specified amount the Company will be
required to apply such proceeds by making an offer to purchase Notes and certain
Indebtedness ranking pari passu in right of payment to the Notes.

         In the case of any redemption of Notes in accordance with the
Indenture, interest installments whose Stated Maturity is on or prior to the
Redemption Date will be payable to the Holders of such Notes of record as of the
close of business on the relevant Regular Record Date or Special Record Date
referred to on the face hereof.  Notes (or portions thereof) for whose
redemption and payment provision is made in accordance with the Indenture shall
cease to bear interest from and after the Redemption Date.
<PAGE>
 
         In the event of redemption of this Note in accordance with the
Indenture in part only, a new Note or Notes for the unredeemed portion hereof
shall be issued in the name of the Holder hereof upon the cancellation hereof.

         If an Event of Default shall occur and be continuing, the principal
amount of all the Notes may be declared due and payable in the manner and with
the effect provided in the Indenture.

         The Indenture permits, with certain exceptions (including certain
amendments permitted without the consent of any Holders and certain amendments
which require the consent of all the Holders) as therein provided, the amendment
thereof and the modification of the rights and obligations of the Company and
any Guarantors and the rights of the Holders under the Indenture and the Notes
and any Guarantees at any time by the Company and the Trustee with the consent
of the Holders of at least a majority in aggregate principal amount of the Notes
at the time Outstanding.  The Indenture also contains provisions permitting the
Holders of at least a majority in aggregate principal amount of the Notes (100%
of the Holders in certain circumstances) at the time Outstanding, on behalf of
the Holders of all the Notes, to waive compliance by the Company and any
Guarantors with certain provisions of the Indenture and the Notes and any
Guarantees and certain past Defaults under the Indenture and the Notes and any
Guarantees and their consequences.  Any such consent or waiver by or on behalf
of the Holder of this Note shall be conclusive and binding upon such Holder and
upon all future Holders of this Note and of any Note issued upon the
registration of transfer hereof or in exchange herefor or in lieu hereof whether
or not notation of such consent or waiver is made upon this Note.

         No reference herein to the Indenture and no provision of this Note or
of the Indenture shall alter or impair the obligation of the Company, any
Guarantor or any other obligor on the Notes (in the event such Guarantor or such
other obligor is obligated to make payments in respect of the Notes), which is
absolute and unconditional, to pay the principal of, premium, if any, and
interest on, this Note at the times, place, and rate, and in the coin or
currency, herein prescribed.

         As provided in the Indenture and subject to certain limitations therein
set forth, the transfer of this Note is registrable in the Note Register, upon
surrender of this Note for registration of transfer at the office or agency of
the Company in the Borough of Manhattan, The City of New York, duly endorsed by,
or accompanied by a written instrument of transfer in form satisfactory to the
Company and the Note Registrar duly executed by, the Holder hereof or its
attorney duly authorized in writing, and thereupon one or more new Notes, of
authorized denominations and for the same aggregate principal amount, will be
issued to the designated transferee or transferees.
<PAGE>
 
         Certificated securities shall be transferred to all beneficial holders
in exchange for their beneficial interests in the Rule 144A Global Notes or the
Regulation S Global Notes if (x) the Depositary notifies the Company that it is
unwilling or unable to continue as depository for such Global Note and a
successor depository is not appointed by the Company within 90 days or (y) there
shall have occurred and be continuing an Event of Default and the Note Registrar
has received a request from the Depositary.  Upon any such issuance, the Trustee
is required to register such certificated Series A Notes in the name of, and
cause the same to be delivered to, such Person or Persons (or the nominee of any
thereof).  All such certificated Series A Notes would be required to include the
Private Placement Legend.

         Series A Notes in certificated form are issuable only in registered
form without coupons in denominations of $1,000 and any integral multiple
thereof.  As provided in the Indenture and subject to certain limitations
therein set forth, the Series A Notes are exchangeable for a like aggregate
principal amount of Notes of a differing authorized denomination, as requested
by the Holder surrendering the same.

         At any time when the Company is not subject to Sections 13 or 15(d) of
the Exchange Act, upon the written request of a Holder of a Series A Note, the
Company will promptly furnish or cause to be furnished such information as is
specified pursuant to Rule 144A(d)(4) under the Securities Act (or any successor
provision thereto) to such Holder or to a prospective purchaser of such Series A
Note who such Holder informs the Company is reasonably believed to be a
"Qualified Institutional Buyer" within the meaning of Rule 144A under the
Securities Act, as the case may be, in order to permit compliance by such Holder
with Rule 144A under the Securities Act.

         No service charge shall be made for any registration of transfer or
exchange of Notes, but the Company may require payment of a sum sufficient to
cover any tax or other governmental charge payable in connection therewith.

         Prior to due presentment of this Note for registration of transfer, the
Company, any Guarantor, the Trustee and any agent of the Company, any Guarantor
or the Trustee may treat the Person in whose name this Note is registered as the
owner hereof for all purposes, whether or not this Note is overdue, and neither
the Company, any Guarantor, the Trustee nor any such agent shall be affected by
notice to the contrary.

         THIS NOTE SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE
LAWS OF THE STATE OF NEW YORK, WITHOUT REGARD TO CONFLICTS OF LAW PRINCIPLES
THEREOF.

         All terms used in this Note which are defined in the Indenture and not
otherwise defined herein shall have the meanings assigned to them in the
Indenture.
<PAGE>
 
                            FORM OF TRANSFER NOTICE

         FOR VALUE RECEIVED, the undersigned registered holder hereby sell(s),
assign(s) and transfer(s) unto

Insert Taxpayer Identification No.  ______________________________________
__________________________________________________________________________
__________________________________________________________________________
(Please print or typewrite name and address including zip code of assignee)
__________________________________________________________________________  the
within Note and all rights thereunder, hereby irrevocably constituting and
appointing
__________________________________________________________________________
attorney to transfer such Note on the books of the Company with full power of
substitution in the premises.  In connection with any transfer of this Note
occurring prior to the date which is the earlier of the date of an effective
Registration Statement or November 3, 1999, the undersigned confirms that
without utilizing any general solicitation or general advertising that:

         [Check One]

         [_]  (a)  this Note is being transferred in compliance with the
exemption from registration under the Securities Act of 1933, as amended,
provided by Rule 144A thereunder or

         [_]  (b)  this Note is being transferred other than in accordance with
(a) above and documents are being furnished which comply with the conditions of
transfer set forth in this Note and the Indenture.  If none of the foregoing
boxes is checked, the Trustee or other Note Registrar shall not be obligated to
register this Note in the name of any Person other than the Holder hereof unless
and until the conditions to any such transfer of registration set forth herein
and in Section 3.07 of the Indenture shall have been satisfied.

Date: ________________________________________________________


NOTICE:  The signature to this assignment must correspond with the name as
written upon the face of the within-mentioned instrument in every particular,
without alteration or any change whatsoever.
<PAGE>
 
Signature Guarantee:

________________________

[Signature must be guaranteed by an eligible Guarantor Institution (banks, stock
brokers, savings and loan associations and credit unions) with membership in an
approved guarantee medallion program pursuant to Securities and Exchange
Commission Rule 17Ad-15.]

TO BE COMPLETED BY PURCHASER IF (a) ABOVE IS CHECKED.  The undersigned
represents and warrants that it is purchasing this Note for its own account or
an account with respect to which it exercises sole investment discretion and
that it and any such account is a "qualified institutional buyer" within the
meaning of Rule 144A under the Securities Act of 1933, as amended, and is aware
that the sale to it is being made in reliance on Rule 144A and acknowledges that
it has received such information regarding the Company as the undersigned has
requested pursuant to Rule 144A or has determined not to request such
information and that it is aware that the transferor is relying upon the
undersigned's foregoing representations in order to claim the exemption from
registration provided by Rule 144A.

Dated:________________________________________________________________

NOTICE:  To be executed by an authorized signatory