Although prehypertension at adolescence is accepted to indicate increased future risk of hypertension, large-scale/long follow-up studies are required to better understand how adolescent blood pressure (BP) tracks into young adulthood. We studied 23 191 male and 3789 female adolescents from the Metabolic Lifestyle and Nutrition Assessment in Young Adults cohort (mean age: 17.4 years) with BP <140/90 mm Hg at enrollment or categorized by current criteria for pediatric BP and body mass index (BMI) values. Participants were prospectively followed up with repeated BP measurements between ages 25 and 42 years and retrospectively between ages 17 and 25 years for the incidence of hypertension. We identified 3810 new cases of hypertension between ages 17 and 42 years. In survival analyses, the cumulative risk of hypertension between ages 17 and 42 years was 3 to 4 times higher in men than in women. Using Cox regression models adjusted for age, BMI, and stratified by baseline BP, the hazard ratio of hypertension increased gradually across BP groups within the normotensive range at age 17 years, without a discernible threshold effect, reaching a hazard ratio of 2.50 (95% CI: 1.75 to 3.57) for boys and 2.31 (95% CI: 0.71 to 7.60) for girls in the group with BP at 130 to 139/85 to 89 mm Hg. BMI at age 17 years was strongly associated with future risk of hypertension even when adjusted to BP at age 17 years, particularly in boys. Yet, BMI at age 30 years attenuated this association, more evidently in girls. In conclusion, BP at adolescence, even in the low-normotensive range, linearly predicts progression to hypertension in young adulthood. This progression and the apparent interaction between BP at age 17 years and BMI at adolescence and at adulthood are sex dependent.