At the direction of the House Committee on Appropriations, the Congressional Budget Office (CBO) has compiled its outlay estimates for the appropriation bills covering fiscal years 1993 through 1997 and compared them, account by account, with actual outlays in those years. This memorandum presents the results of that analysis. In aggregate over the five-year period, CBO's estimates of outlays for appropriation bills have been almost identical to the actual totals-coming within 0.1 percent of discretionary outlays during that period. The yearly estimates have been off, in one direction or the other, by an average of less than 0.4 percent. Although the sources of errors vary from year to year, some overall patterns are apparent. In particular, CBO's estimates of defense spending tended to be too low, but its projections of nondefense outlays were too high in each of the five years. Estimates for individual accounts were less accurate than the totals, and the small aggregate error each year was the result of deviations in both directions for hundreds of accounts. The median absolute error, which disregards whether the error was positive or negative, was about 6 percent for individual accounts of $50 million or more.