[Cancer in adult twins]

Previous reports on twin cancer have been reviewed. Especially, cancer in later adulthood has been focused. There have been done several large scale twin studies on cancer in Europe and the U.S.A., but not in Japan. Although, it is not easy to establish twin registry in Japan, the importance of twin study in epidemiology and preventive medicine has been emphasized. Methodology of twin research in epidemiology has been described. Epidemiological research methods in Japan have been described through the authors' past experience.