The deaths of 100 men due to coronary artery disease which occurred so suddenly and unexpectedly as to merit a coroner's necropsy have been studied, with special reference to the exact circumstances of their occurrence. The most significant relationship of sudden death was with acute psychological stress. Moderate physical activity, the time of day, the day of the week, and a recent meal, especially if accompanied by alcohol, were also significantly related. Very strenuous exercise, the season of the year, the environmental temperature or recent change of it, and chronic psychological stress were not so related. Neither were the actual smoking of a cigarette nor the composition of the meal immediately preceding death. Compared with previous series of proved acute myocardial infarction the necropsies in these cases showed that the right coronary artery had been recently occluded by a thrombus more often than the left anterior descending. Stenosis or occlusion of the right coronary artery bore a significant relation to the suddenness of death. Special analysis of the 52 cases in which neither recent thrombus nor infarction were found did not disclose any circumstances attending death which differed from the remainder. Some comparisons are made with the circumstances attending the onset of symptoms in 100 men studied while recovering from an acute myocardial infarct.