The Karunagappally Cohort Study began in 1990 as a cohort of nearly all residents of Karunagappally, India, and was established to examine the potential health effects of high background radiation (HBR) on cancer risk in relation to individual cumulative radiation dose. During the years of 1990 to 1997, house-to-house visits were conducted to measure indoor and outdoor radiation levels and to collect personal information using a 6-page standardized questionnaire that included questions on socio-demographic factors, lifestyle, dietary habits, and tobacco and alcohol use. In total, this household survey collected personal information on over 350,000 subjects across 71,674 households, which corresponds to 93% of the population and 94% of households in Karunagappally.