The agency said 115,478 taxpayers did not get a refund check - in some cases it was more than one check - averaging about $953. The money can be claimed as soon as taxpayers update their addresses with the IRS.

"Taxpayers should not miss out on getting their money back," said Richard Morgante, commissioner of the IRS Wage and Investment division.

The IRS in 2007 has processed nearly 105 million refunds either by mail or direct deposit in 2007, totaling about $240 billion. Undeliverable refunds make up about one-tenth of 1 percent of all refunds, or about one in 1,000.

The list of taxpayers with undeliverable refund checks went up about 21 percent from 2006, an increase due in part to the Telephone Excise Tax Refund. That money was a one-time refund from the long-distance excise tax that the government stopped collecting last August.

The IRS directed people who never got expected checks to the "Where's My Refund?" site on its home page, http://www.irs.gov They can also call 1-800-829-1954.