Background: Not enough is known about the association between blood pressure (BP) in adolescence and future cardiovascular events. Objective: To measure this association using the 2017 American College of Cardiology/American Heart Association guidelines for classifying BP elevation. Design: Cohort study. Setting: Sweden. Participants: Males in late adolescence who were conscripted into the military from 1969 to 1997. Measurements: Baseline BP was measured at conscription. The primary outcome was a composite of cardiovascular death or first hospitalization for myocardial infarction, heart failure, ischemic stroke, or intracerebral hemorrhage. Results: The study included 1 366 519 males with a mean age of 18.3 years. The baseline BP was classified as elevated (120 to 129/<80 mm Hg) for 28.8% of participants and hypertensive (≥130/80 mm Hg) for 53.7%. During a median follow-up of 35.9 years, 79 644 had a primary outcome. The adjusted hazard ratio was 1.10 for elevated BP (95% CI, 1.07 to