There are several high-background radiation areas (HBRAs) in Yangjiang of Guangdong Province, China, and Karunagappally of Kerala State, India. In order to evaluate the health effects of high natural radiation, epidemiological studies have been conducted by local scientists. Currently, these studies are continued with the help of Japanese researchers. In this paper, their results will be reviewed. In Yangjiang, China, there are two HBRAs, ie, Tongyou and Dong-anling, located in the west and east of Yangjiang area, respectively. In the 1970s, Dr LX Wei and his colleagues started the cancer mortality study among the residents in those HBRAs and its neighboring control areas selected from two counties, Enping and Taishan (1). The major results obtained from their study were published in 1980 (1). In 1991, a collaborative study involving Chinese and Japanese research groups began. The study groups in the two countries are led by Drs. LX Wei and T. Sugahara, respectively (2). This international collaborative study has two new features. First, the study group established a fixed cohort whose members resided in the HBRA and the control areas as of 31 December 1986. Second, the control area was restricted to the one in Enping County, which shares its eastern border with Yangjiang City, the political and economic center of Yangjiang area. The study area excluded from the new study was the control area in Taishan, which is located to the east of Enping and is 300 kilometers away from Guangzhou City, the capital of Guangdong Province (3). Recently, they conducted a series of case-control studies in order to evaluate the confounding effects of life styles and other factors on the radiation-related risk estimation of leukemia, and cancer of the lung and nasopharynx. The results obtained from the study on nasopharyngeal cancer were published, recently (4). In the south-western part of Indian subcontinent, there is an HBRA in Karunagappally Taluk of Kerala State, India. In view of radiation levels and population sizes, this area is one of the most important HBRAs in the world. The taluk, consisting of 12 districts or panchayat, has the population of about 400,000 or about 70,000 families according to 1991 census. The radiation levels are particularly high in the taluk’s coastal area. In Karunagappally, the research group led by K Nair conducted an enormous work, including questionnaire survey of every resident in the taluk (5, 6). One of the advantages of this area is the existence of tumor registry established in 1990. Cancer incidence obtained from the registry was published in the Cancer Incidence in the Five Continents (7). In 1999, a collaborative study involving Indian and Japanese research groups started.