EXHIBIT 15.1

April 14, 2004

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

We are aware of the incorporation by reference in the Registration Statement (Form S-8) of Sun Microsystems, Inc. pertaining to the Kealia, Inc. Amended and Restated 2001 Stock Plan of our reports dated October 15, 2003 and January 14, 2004 relating to the unaudited condensed consolidated interim financial statements of Sun Microsystems, Inc. that are included in its Form 10-Q for the quarters ended September 28, 2003 and December 28, 2003.

Pursuant to Rule 436(c) of the Securities Act of 1933 our reports are not a part of the registration statement 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