The Ohasama Study is a long-term prospective cohort study of the general population in the town of Ohasama (currently, Hanamaki city) in Iwate Prefecture, Japan, that was started in 1986. Ohasama is a typical farming village in the Tohoku region that consists of part-time farming households that cultivate mainly fruit trees. At the start of the study, the prevention of hypertension, a main cause of strokes, was taken to be an important issue in public health activities because of the many people who died or needed care as a result of strokes in Ohasama. A home blood pressure measurement program was then begun with the aim of preventing hypertension while increasing a sense of solidarity among community residents and the awareness that “one must protect one’s own health.” As a result, this project became the world’s first community-based epidemiological study using home blood pressure, as well as 24-hour ambulatory blood pressure, for which measurements were also initiated. In the 1990s, the Ohasama Study reported a linear “the lower, the better” relationship between out-of-office blood pressure and cardiovascular risk. To date, we have accumulated advanced evidence regarding the clinical significance of out-of-office blood pressure. Those have contributed to hypertension management guidelines around the world. This article summarizes the results of representative long-term follow-up studies of the Ohasama Study.