Male breast cancer is rare. The total number of incidence in Osaka for the period of 1966-95 was 182. Male-to-female ratio for breast cancer incidence was 1:164 in Osaka during this period. Mean age of the male breast cancer incidence was 63.3. The numbers of incidence and the crude incidence rates for male breast cancer have increased during the last 3 decades, while the age-standardized rates have remained constant. The age-specific incidence rates for males showed a gradual increase with age, while those for females showed a steep increase beginning at twenty years of age and a peak around 45-49 or 50-54 years old. The age-standardized incidence rates of male breast cancer were lower in Japan than in European countries and North America, as were those of female breast cancer. Distributions of the histological type and the extent of disease were not significantly different between males and females. Relative 5-year survival for the male breast cancer was, however, lower than that for the female, especially in the "regional" stage and "distant" stage. Further studies on the sex-difference in survival will be mandatory based on high-quality hospital cancer registries' data, which provide detailed information on the clinical stage and treatment. J Epidemiol, 2001 ; 11 : 1-7