A 31-year-old white man collapsed suddenly at a graduation ceremony and was pronounced dead after attempted resuscitation. He had no pertinent medical or familial history. Postmortem toxicologic studies showed negative results. A complete autopsy revealed a cardiac cause of death. Grossly, the right ventricular chamber was moderately to markedly dilated, and its free wall showed extensive myocardial adiposity. Microscopically, the right ventricular free wall consisted predominantly of adipose tissue, with only small subendocardial islands of hypertrophied myocytes and interstitial fibrosis. These features are characteristic of arrhythmogenic right ventricular cardiomyopathy. Moreover, Purkinje-like cells were observed among right ventricular myocytes and may have increased the likelihood of developing an arrhythmia. To our knowledge, this finding has not been previously emphasized. Because arrhythmogenic right ventricular cardiomyopathy accounts for 10% of cases of sudden unexpected cardiac death, recognition of this disease by pathologists is important, especially in cases of otherwise unexplained death in young persons.