This study examined the association between romantic relationships and delinquency in adolescence and young adulthood. Using a large, longitudinal, and nationally representative sample, results from negative binomial regressions showed a positive association between romantic involvement and delinquency in adolescence. Furthermore, the cumulative number of romantic relationships from adolescence to young adulthood was positively related to delinquency in young adulthood even after controlling for earlier delinquency in adolescence. These analyses also controlled for the effects of participants' gender, age at initial assessment, puberty, race/ethnicity, and other demographic characteristics (e.g., family structure and parents' education). Findings are discussed in terms of their implications for understanding the role of romantic relationships in the development of young people and for stimulating future research questions.