Pathologic features that characterize hypertrophic cardiomyopathy (HC) in exertional versus nonexertional sudden deaths have not been extensively studied. We performed gross measurements and histologic analysis on 103 autopsy cases of HC and correlated these with clinical findings. Pathologic features of the 71 sudden deaths were compared between exertional and nonexertional deaths. Age at death was significantly younger in exertional (27 ± 13 years) versus nonexertional sudden deaths (40 ± 16 years, p = 0.0003). Exertional deaths were more likely in women (35 of 37) versus sudden deaths at rest (21 of 34, p = 0.0002). There was no significant difference in the incidence of syncope in the exertional sudden deaths (14%) compared to the nonexertional sudden deaths (9%, p = 0.5) or in the rate of a previous diagnosis of HC (21% vs 21%, respectively). Mean heart weight was significantly decreased in exertional sudden deaths versus nonexertional sudden deaths. There was no difference in the frequency of left ventricular outflow tract plaque (54% exertional vs 46% nonexertional, p = 0.06). By multivariate analysis, including all categories of HC, only decreased heart weight (p = 0.02) and male gender (p = 0.002) were significantly associated with exertional sudden death. In conclusion, there are no pathologic features that would identify patients with HC at risk for exertional death. Because relatively decreased heart weight is strongly associated with exertional death, and because a large proportion of exertional deaths with HC are not associated with significant asymmetry, cardiologists should be careful in excluding the diagnosis of HC in athletes with even mild degrees of cardiomegaly, especially young men.