In this, article we use a nationally representative longitudinal sample of middle and high school teenagers to examine the association between having sex at a young age with an older partner and selected outcomes during the transition to young adulthood. Using data from the National Longitudinal Study of Adolescent Health (Add Health), which allow us to control for a range of individual and family characteristics, we address the following research questions: First, is having sex at a young age with an older partner associated with the risk of acquiring STDs or being involved in a teenage or nonmarital birth by young adulthood? Second, are any observed associations affected by characteristics of teenagers’ relationship history? Finally, do associations differ for males and females?