Epidemiological studies on several selected topics in occupational health in Japan is introduced in the present paper. Karoushi or sudden death due to overwork was proposed in 1978. Hypertension was suggested to be one of the risk factors for Karoushi, although the risk factors related only to work conditions have not been clarified yet. Epidemiological studies on occupational stress and stress-related diseases have been developed, even with the difficulties of definition or measurement of occupational stress. The depression state and mental state were influenced by occupational stress and personality. A large scale cohort study on 180 thousand radiation workers in Japan has been conducted since 1990 in order to obtain scientific information on the health effects due to low dose protracted radiation exposure. In order to assess occupational cancer risk due to hazardous working environment in Japan, several epidemiological studies were carried out. One cohort study on Japanese forest workers for vibration syndrome showed that the latent interval for the development of vibration induced white finger was 6.2 years. Finally, evaluation studies of mass cancer screening programs in Japan were introduced. It was stressed that the epidemiological approach should be strengthened more in order to obtain more information for prevention of occupational diseases or work-related diseases and for the promotion of workers' health.