EXHIBIT 15.1

November 3, 2004

The Board of Directors and Stockholders, Sun Microsystems, Inc.

We are aware of the incorporation by reference in the Registration Statements (Form S-8 Nos. 33-9293, 33-11154, 33-15271, 33-18602, 33-25860, 33-28505, 33-33344, 33-38220, 33-51129, 33-56577, 333-01459, 333-09867, 333-15179, 333-34543, 333-34651, 333-38163, 333-40677, 333-40675, 333-59503, 333-62987, 333-65531, 333-67183, 333-72413, 333-86267, 333-89391, 333-90907, 333-35796, 333-45540, 333-48080, 333-49788, 333-52314, 333-56358, 333-59466, 333-61120, 333-62034, 333-68140, 333-73218, 333-98097, 333-100189, 333-101332, 333-101323, 333-102920, 333-108639 and 333-109303, 333-111968, 333-114550 and 333-114551; and Form S-3 Nos. 333-81101 and 333-63716) of Sun Microsystems, Inc. of our report dated November 3, 2004 relating to the unaudited condensed consolidated interim financial statements of Sun Microsystems, Inc. that are included in its Form 10-Q for the quarter ended September 26, 2004.

Pursuant to Rule 436(c) of the Securities Act of 1933 our report is not a part of the registration statements prepared or certified by accountants within the meaning of Section 7 or 11 of the Securities Act of 1933.

Very truly yours,

/s/ Ernst & Young LLP