The descriptive epidemiology of sudden nontraumatic death from persons aged 1 to 21 years was studied in a defined population. In nine years, the 207 deaths in this group (4.6/100,000 population/per year) comprised 22% of nontraumatic mortality. Age-specific rates were highest between 1 and 4 years (mainly infections and undetermined causes) and 14 and 21 years (mainly cardiovascular, epilepsy, intracranial hemorrhage, and asthma). Nonwhite rates were higher than whites, and white males had higher rates than white females. Referral for medicolegal evaluation was inconsistent. Only 18% died at university hospitals. Infections included lower respiratory tract and septic shock. The main cardiac diagnosis was myocarditis. Most epilepsy deaths were unwitnessed and had absent or low anticonvulsant levels. Eighty-five cases had a known associated chronic illness and 111 reported prodromal symptoms. Prevention of these events requires improved identification and management of antecedent conditions.