Between June 1981 and February 1983, the Centers for Disease Control (Atlanta) received reports of 1,000 patients living in the United States who met a surveillance definition for the acquired immune deficiency syndrome (AIDS). Seventy-three percent of these patients were diagnosed after January 1, 1982. The 1,000 patients included 284 with Kaposi's sarcoma (KS), 497 with Pneumocystis carinii pneumonia (PCP), 83 with KS and PCP, and 136 with opportunistic infections other than PCP. The overall mortality has been 39.2%. Cases have been reported from 32 states and the District of Columbia; New York, California, New Jersey, and Florida account for 82.7% of the reports. All but 61 of the patients could be classified into one or more of the following groups: homosexual or bisexual men, intravenous drug abusers, Haitian natives, or patients with hemophilia. Epidemiologic trends in AIDS cases are consistent with the gradual extension of an infectious agent into new populations.