Two hundred and three Karoshi victims who suffered cardiovascular attacks and for whom workers' compensations was claimed were surveyed. These cases were 196 males and 7 females in middle age, and comprised 123 strokes, 50 acute cardiac failures, 27 myocardial infarctions and 4 aortic ruptures. As a sociomedical background, it was shown that two-thirds of them were working for long hours such as more than 60 hr per week, more than 50 hr overtime per month, or more than half of their fixed holidays before the attack. Moreover, among the white-collar workers, these long working hours were accompanied with other stressful work issues such as career problems, excessive business trips, strident norms, and changes of work places; among the blue-collar workers, they were accompanied with those such as irregular midnight work, insufficient manpower and long-distance driving, etc. On the other hand, eighty-eight cases of them experienced several minor and sudden events including work-related emotional anxiety or excitement, rapid increase of workload, unexpected work trouble or environmental changes of work places anticipated at least within 24 hr directly before the attack. It was concluded that Karoshi, meaning fatal attacks by overload, was one of the work-related diseases mainly triggered by long working hours.