The occurrence of hypertension and its precursors is examined in the Framingham Offspring Study of 2,027 men and 2,267 women ages 20-49 years followed for 8 years. The age-specific prevalence of hypertension was similar at both the first (1971-1975) and the second (1979-1983) examination for both men and women. Prevalence rates were higher among men than among women, and there was a higher rate of hypertension treatment at the second exam, particularly among women, 75% of whom reported being treated for hypertension. The incidence of hypertension in participants free from hypertension at the first examination increased threefold from the second to the fifth age decades in men and eight-fold in women. Under age 40, men were twice as likely as women to develop hypertension, but after age 40, 8-year incidence rates were similar in men (14.2%) and women (12.9%). Adiposity, relative weight, heart rate, alcohol intake, hematocrit, blood sugar, serum protein, triglyceride, and phosphorous were all related to hypertension occurrence in one or both sexes, controlling for age. In multivariate analysis, adiposity (P less than 0.01), heart rate (P less than 0.01), and triglyceride (P less than 0.05) were all significant independent predictors of hypertension in men. In women, adiposity (P less than 0.001), heart rate (P less than 0.01), hematocrit (P less than 0.05), and alcohol consumption (P less than 0.05) were independent contributors. When controlling for blood pressure measured at the first examination, the best single predictor of hypertension incidence, the multivariate assessment changed very little. Adiposity stands out as a major controllable contributor to hypertension. Changes in body fat over 8 years were related to changes in both systolic and diastolic blood pressure. Markedly obese women in their fourth decade were seven times more likely to develop hypertension than were lean women of the same age. Weight control deserves a high priority in efforts to prevent hypertension in the general population.