The objective of this study was to evaluate the incidence and correlates of sudden unexpected nontraumatic death among young adults in a well-surveyed population. The incidence and pathogenesis of sudden unexpected nontraumatic death in a young adult population (aged 20 to 40 years old) have not been well defined. All residents 20 to 40 years old from Olmsted County, Minnesota, who had nontraumatic sudden death between 1960 and 1989 were included. Histologic and gross cardiac specimens were examined. The incidence of sudden death was estimated based on the ratio of number of observed events to relative census data for the Olmsted County population from the last 3 decades. Statistical comparisons between age decades were obtained with the chi-square test. Incidence trends were tested using Poisson regression. Of the 54 subjects, 19 were women (4.1/10(5) population annually) and 35 were men (8.7/10(5) population annually). An increase in incidence of sudden death was evident in men. Causes of death included coronary artery disease, noncardiovascular disease, suspected primary arrhythmia, vascular disease, myocarditis, hypertrophic cardiomyopathy, and unknown causes. Gross and histologic features suggestive of right ventricular dysplasia were found in 9 subjects (17%), but 6 of these 9 had other established causes of death. Of the 27 sudden deaths between 1980 and 1989, 9 (33%) had a history of cocaine abuse. A trend in increasing incidence of sudden death in young men is noted. A high prevalence of cocaine abuse was observed in young adults who died suddenly. Histologic features of right ventricular dysplasia were prevalent but were not necessarily the primary cause of death.