Sudden infant death syndrome (SIDS) is "the sudden death of an infant under 1 year of age which remains unexplained after a thorough case investigation, including performance of a complete autopsy, examination of the death scene, and review of the clinical history." Although SIDS is a diagnosis of exclusion and of unknown etiology, it is the leading cause of postneonatal mortality in the United States, accounting for approximately one-third of all such deaths. This report analyzes age-, race-, and region-specific trends for SIDS in the United States during 1983-1994 (the latest year for which final data are available) and indicates that annual rates of SIDS declined more than three times faster during 1990-1994 than during 1983-1989.