During 1993, local, state, and territorial health departments reported 103,500 acquired immunodeficiency syndrome (AIDS) cases among persons aged > or = 13 years in the United States, an increase of 111% over the 49,016 reported in 1992 (Figure 1). This increase resulted from the expansion of the AIDS surveillance case definition in 1993*; in comparison, the number of cases based on the preexisting case definition decreased slightly. This report summarizes characteristics of persons reported with AIDS in 1993, compares these findings with data from 1992, and describes the impact of the change in the AIDS surveillance definition on AIDS case reporting.