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Objective: Breast and ovarian cancer is rare in Japan compared with other developed countries but their mortality rates are increasing. It is necessary to examine the experience of Japan as a guide to further prevent breast and ovarian cancer in our country. Methods: We conducted an epidemiological study of breast and ovarian cancer in the past 50 years to investigate the trends and characteristics of the mortality rates in Japan. The numbers of age-specific death from breast and ovarian cancer and the population of 5-year groups were obtained from the Vital Statistics of Japan. The truncated age specific mortality rates were calculated according to the patterns of age specific mortality rates from both cancers. Age adjustments were made to the standard world population. Results: In the past 50 years, mortality rates of breast and ovarian cancer increased about 2 or 6 fold, respectively. This increase was most marked over 50 years old. The death pattern of breast cancer was same as that of ovarian cancer, but that of ovarian cancer changed greatly with time. The birth cohort study had some interesting findings. Common to breast and ovarian cancer, the later the year of birth, the higher the mortality rates from both malignancies in later life. Conclusion: The increase of the yearly mortality rates from breast and ovarian cancer might be due to changes in lifestyle and environmental factors. We are very concerned about dietary practices. Further investigation is needed to clarify the possible causes of animal food.