U.S. Centers for Disease Control and Prevention (CDC) describes cases of a rare lung infection, Pneumocystis carinii pneumonia (PCP), in five young, previously healthy gay men in Los Angeles. These men have other unusual infections as well, indicating that their immune systems are not working; two have already died by the time the report is published. This edition of the MMWR marks the first official reporting of what will become known as the AIDS epidemic.