OBJECTIVE: We sought to examine the relation between physical activity and incident hypertension in young adults over 15 years of follow-up in the Coronary Artery Risk Development in Young Adults study. METHODS: A total of 3993 Black and White men and women aged 18 to 30 years were examined at baseline, and 2, 5, 7, 10, and 15 years later. Blood pressure and physical activity were measured at each exam. Hypertension was defined as systolic 140 mm Hg or higher, diastolic 90 mm Hg or higher, or antihypertensive medication use. Average physical activity and incident hypertension over 15 years of follow-up were analyzed. RESULTS: There were 634 cases of incident hypertension over 15 years of follow-up. Those who were more versus less physically active experienced a reduced risk (hazard rate ratio = 0.83; 95% confidence interval = 0.73, 0.93) for incident hypertension, after adjustment for race, sex, age, education, and family history of high blood pressure. CONCLUSIONS: Physical activity merits attention in the prevention of incident hypertension among young adults, particularly as they move into middle age.