To establish guidelines for individuals with hypertrophic cardiomyopathy (HCM) to follow in their daily lives and minimize the chance of sudden death (SD), circumstances of SD in 24 autopsied definite HCM cases were compared with those with 905 autopsied cases of other heart diseases. Circumstances of symptoms experienced in daily activities of 35 age-matched surviving HCM cases were also studied. In the autopsied HCM cases, SD occurred during exertion more frequently (79.2%) than in the other autopsied cardiac patients (22.7%). Sudden changes in pace or movement accompanied by mental excitement, such as hurrying to board a train, were more frequent causes of SD in HCM (47.4%) than in other cardiac patients (8.3%). In the surviving HCM cases, symptoms of distress occurred frequently during very hard work or with sudden rapid movement. Thus, one probable daily guideline for HCM sufferers would appear to be not only to eliminate very hard work but also to lead mentally and physically quiet and relaxed life.