Exhibit 5.1

                  LEGAL OPINION AND CONSENT OF COMPANY COUNSEL

McGuireWoods LLP
1345 Avenue of the Americas, 7th Floor
New York, New York 10105

February 12, 2007

Board of Directors
Diomed Holdings, Inc.
One Dundee Park
Andover, MA 01810

Ladies and Gentlemen:

We are acting as counsel to Diomed Holdings, Inc., a Delaware corporation (the
"Company"), in connection with the filing with the Securities and Exchange
Commission (the "Commission"), under the Securities Act of 1933, as amended (the
"Act"), of the Registration Statement on Form SB-2/A (the "Registration
Statement") relating to the offer and sale pursuant to the Registration
Statement, by the Selling Stockholders identified in the Registration Statement,
of up to 1,800,000 shares of common stock, par value $0.001 per share, of the
Company (the "Shares"), which shares of common stock are issuable by the Company
upon exercise of the common stock purchase warrants issued September 30, 2005
(without giving effect to the increased number of underlying shares as a result
of antidilution adjustments resulting from the September 29, 2006 issuance of
the Preferred Stock). This opinion letter is furnished to you for filing with
the Commission pursuant to Item 601 of Regulation S-K promulgated under the Act.

In reaching the opinion stated in this letter, we have reviewed originals of
copies of the Registration Statement, the Certificate of Incorporation and the
Bylaws of the Company, both as amended to date, and such other documents as we
have considered relevant. We have assumed that (i) all information contained in
all documents reviewed by us is correct, (ii) all signatures on all documents
reviewed by us are genuine, (iii) all documents submitted to us as originals are
true and complete, (iv) all documents submitted to us as copies are true and
complete copies of the originals thereof, (v) each natural person signing any
document reviewed by us had the legal capacity to do so and (vi) each natural
person signing in a representative capacity any document reviewed by us had
authority to sign in such capacity.

Based upon the foregoing, it is our opinion that the Shares, when issued in the
manner described in the Registration Statement, will be duly authorized, validly
issued, fully paid and nonassessable.

The opinion expressed above is limited to matters governed by the laws of the
State of Delaware. We express no opinion herein about the effect of federal or
state securities laws or the laws of any other jurisdiction.

We hereby consent to the use of this opinion letter as Exhibit 5.1 to the
Registration Statement and to the use of our name under the heading "Legal
Matters" therein. In giving this consent, we do not admit that we are in the
category of persons whose consent is required under Section 7 of the Act or the
rules and regulations of the Commission promulgated thereunder.

This opinion letter speaks as of the date hereof. We disclaim any duty to advise
you regarding any change subsequent to the date hereof in, or to otherwise
communicate with you with respect to, the matters addressed herein.

Very truly yours,

/s/  McGuireWoods LLP