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                                                                     EXHIBIT 5.1

                                HALE AND DORR LLP
                               Counsellors At Law
                  60 State Street, Boston, Massachusetts 02109
                         617-526-6000 * FAX 617-526-5000


                               September 15, 2000

NEON Communications, Inc.
2200 West Park Drive
Westborough, Massachusetts 01581

         Re:      Amended and Restated 1998 Stock Incentive Plan
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Ladies and Gentlemen:

         We have assisted in the preparation of a Registration Statement on Form
S-8 (the "Registration Statement") to be filed with the Securities and Exchange
Commission (the "Commission") under the Securities Act of 1933, as amended (the
"Securities Act"), relating to an aggregate of 4,453,276 shares of Common Stock,
$0.01 par value per share (the "Shares"), of NEON Communications, Inc., a
Delaware corporation (the "Company"), issuable under the Company's Amended and
Restated 1998 Stock Incentive Plan, as amended (the "Plan").

         We have examined the Certificate of Incorporation, as amended, and
Bylaws of the Company, each as amended and restated to date and originals, or
copies certified to our satisfaction, of all pertinent records of the meetings
of the directors and stockholders of the Company, the Registration Statement and
such other documents relating to the Company as we have deemed material for the
purposes of this opinion.

         In our examination of the foregoing documents, we have assumed the
genuineness of all signatures, the authenticity of all documents submitted to us
as originals, the conformity to original documents of all documents submitted to
us as copies, the authenticity of the originals of such latter documents and the
legal competence of all signatories to such documents.

         We assume that the appropriate action will be taken, if any is
required, prior to the offer and sale of the Shares in accordance with the Plan,
to register and qualify the Shares for sale under all applicable state
securities or "blue sky" laws.

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         We express no opinion herein as to the laws of any state or
jurisdiction other than the state laws of The Commonwealth of Massachusetts, the
Delaware General Corporation Law statute and the federal laws of the United
States of America.

         Based upon and subject to the foregoing, we are of the opinion that the
Shares have been duly authorized for issuance and, when the Shares are issued
and paid for in accordance with the terms and conditions of the Plan, the Shares
will be validly issued, fully paid and nonassessable.

         It is understood that this opinion is to be used only in connection
with the offer and sale of the Shares while the Registration Statement is in
effect.

         Please note that we are opining only as to the matters expressly set
forth herein, and no opinion should be inferred as to any other matters.

         We hereby consent to the filing of this opinion with the Commission as
an exhibit to the Registration Statement in accordance with the requirements of
Item 601(b)(5) of Regulation S-K under the Securities Act. In giving such
consent, we do not hereby admit that we are in the category of persons whose
consent is required under Section 7 of the Securities Act or the rules and
regulations of the Commission.

                                             Very truly yours,

                                             /s/ Hale and Dorr LLP

                                             HALE AND DORR LLP