The Ni-Hon-San study began in 1965 to compare coronary heart disease and its risk factors among Japanese men in Hiroshima and Nagasaki (Japan), Honolulu (Hawaii), and the San Francisco Bay Area (California). The Japan cohort included 2,141 men selected from the Adult Health Study (AHS) in Hiroshima and Nagasaki. Participants had been assessed biennially since 1958 and participated in the baseline Ni-Hon-San assessments from 1965 to 1966. The Hawaii cohort included 8,006 Japanese men living on Oahu, Honolulu, who participated in the Honolulu Heart Program and were assessed at baseline from 1965 to 1968. The California cohort included 1,844 Japanese American men living in eight counties of the San Francisco Bay Area. Participants were recruited through a 1967 census and examined at baseline from 1969 to 1970. All participants were born between 1900 and 1919. Follow-up in Japan includes biennial reexaminations and mortality surveillance. In Hawaii, follow-up includes assessments at two and six years after baseline, and routine hospital and mortality surveillance. In California, mortality surveillance was maintained for two years.