Of 21 sudden deaths in sportsmen, 18 were thought to be caused by heart attacks either during or after sport. There was firm evidence of ischaemic heart-disease in 9, strongly suggestive evidence in 7, but in 2 there was only suggestive clinical evidence. As a group, these subjects were characterised by (1) a mean age above thirty (above twenty-five for rugby players); (2) a family history of early heart-attacks; and (3) antecedent symptoms of chest pain or pressure in 9, fatigue or blackout in 4, and minor complaints in 2. Most were known to their medical practitioners. Psychological factors were thought to be important in 8. Doctors, players and referees should be aware that severe sporting exertion as in rugby football involves a risk which for most players is relatively minor, but in the minority predisposed to heart-attacks by family history, smoking, or age (as in referees) the risk is more serious. To reduce hazard of sudden death in exercise, players and referees should be warned against smoking and informed of the serious implications of the development of chest pain, pressure, or undue tiredness before, during, or after sport.