As part of its commemoration of CDC's 50th anniversary, MMWR is reprinting selected MMWR articles of historical interest to public health, accompanied by a current editorial note. <i>On June 4, 1981</i>, MMWR<i>published a report about</i>Pneumocystis carinii<i>pneumonia in homosexual men in Los Angeles. This was the first published report of what, a year later, became known as acquired immunodeficiency syndrome (AIDS). This report and current editorial note appear below</i>. IN THE PERIOD October 1980-May 1981,5 young men, all active homosexuals, were treated for biopsy-confirmed<i>Pneumocystis carinii</i>pneumonia at 3 different hospitals in Los Angeles, California. Two of the patients died. All 5 patients had laboratory-confirmed previous or current cytomegalovirus (CMV) infection and candidal mucosal infection. Case reports of these patients follow. Patient 1: A previously healthy 33-year-old man developed<i>P. carinii</i>pneumonia and oral mucosal candidiasis in March 1981 after a 2-month history of fever associated