Introduction: Prehypertension defined as blood pressure (BP) 120-139/80-89 mmHg, has a prevalence of 23% in U.S. young adults (age 20-39 years). Young adult high diastolic blood pressure (DBP) has been associated with later life coronary heart disease (CHD), but it is unclear if lifelong benefits of early blood pressure control outweigh costs and side-effect risks. Objective: We estimated CHD events and life-long cost-effectiveness of U.S. Preventive Service Task Force recommended lifestyle modification (LM) or pharmacotherapy in young adults with DBP ≥80mmHg, incremental to later life hypertension treatment. Methods: A microsimulation model simulated CHD events from age 20 until death for 20-year olds selected from 1999-2014 NHANES. Individual risk factor trajectories were assigned, and risk functions predicted CHD based on Framingham Offspring Study data, accounting for both age 20-39 time-weighted average DBP and later life systolic blood pressure (SBP). Simulated interventions lowered DBP ≥80mmHg for age 20-39 years, and SBP ≥140mmHg for age ≥40 years. Cost-effectiveness was measured as incremental cost-effectiveness ratios (ICERs) and net health benefit (NHB) at willingness to pay (WTP) threshold $50,000/quality adjusted life year (QALY). Results: In 40,000 young adults with DBP ≥80 mmHg (50% women), pharmacologic BP control in young adulthood and later life prevented the most CHD events (Table). The strategy that yielded highest NHB in women was pharmacologic control after age 40 (ICER $26,536/QALY). In men, lifestyle modification to control DBP in young adulthood plus pharmacotherapy for later life hypertension (ICER $42,481/QALY) yielded highest NHB. Conclusion: Early DBP control in young adults could achieve substantial health benefits over the life course but standard interventions to achieve this goal are costly. Innovative strategies to reduce pharmacotherapy costs and improve sustainability of lifestyle modification could make early BP control a higher-value prevention strategy in young adults.