The Japan Public Health Center-based Prospective Study on Cancer and Cardiovascular Diseases (JPHC Study; formerly called "Koseisho Multipurpose Prospective Cohort Study") began in 1990 (Cohort I) and 1993 (Cohort II). The JPHC Study covers 11 public health center areas throughout Japan and includes a total of 140,420 residents. The study's design includes a baseline survey with a self-administered questionnaire on lifestyle and collection of blood and health checkup data; a follow-up system for mortality, migration, and incidence of cancer and cardiovascular diseases; an additional follow-up survey after 5 and 10 years; and distribution of a newsletter. The JPHC study is expected to provide evidence for the prevention and control of cancer and cardiovascular diseases in the 21st century.