EXHIBIT 5.1

                                ROPES & GRAY LLP

December 30, 2004

ViaCell, Inc.
245 First Street
Cambridge, MA 02142

Ladies and Gentlemen:

This opinion is furnished to you in connection with a registration statement on
Form S-1 (File No. 333-114209) (the "REGISTRATION STATEMENT"), filed with the
Securities and Exchange Commission under the Securities Act of 1933, as amended
(the "ACT"), for the registration of up to 8,625,000 shares of Common Stock,
$0.01 par value (the "SECURITIES"), of ViaCell, Inc., a Delaware corporation
(the "COMPANY"), including any Securities issuable upon exercise of the
over-allotment option granted by the Company.

The Securities are to be sold pursuant to an underwriting agreement (the
"UNDERWRITING AGREEMENT") to be entered into by and among the Company, on the
one hand, and, on the other hand, Credit Suisse First Boston LLC and UBS
Securities LLC, as representatives of several underwriters named in the
Underwriting Agreement, the form of which has been filed as Exhibit 1.1 to the
Registration Statement.

We have acted as counsel for the Company in connection with its proposed
issuance of the Securities. For purposes of this opinion, we have examined and
relied upon such documents, records, certificates and other instruments as we
have deemed necessary.

The opinion expressed below is limited to Delaware General Corporation Law,
including the applicable provisions of the Delaware Constitution and the
reported cases interpreting those laws.

Based upon and subject to the foregoing, we are of the opinion that the
Securities have been duly authorized for issuance, and, when the Securities are
issued and sold and the Company has received the consideration therefor in
accordance with the terms of the Underwriting Agreement, the Securities will be
validly issued, fully paid and non-assessable.

We understand that this opinion is to be used in connection with the
Registration Statement. We hereby consent to the filing of this opinion as part
of the Registration Statement and to the use of our name therein and in the
related prospectus under the caption "Legal Matters." In giving such consent, we
do not thereby admit that we are in the category of persons whose consent is
required under Section 7 of the Act.

Very truly yours,

/s/ Ropes & Gray LLP

Ropes & Gray LLP