The present study compared two theories of the association between romantic involvement and adjustment: a social timetable theory and a developmental task theory. We examined seven waves of longitudinal data on a community based sample of 200 participants (Wave 1 mean age = 15 years, 10 months). In each wave, multiple measures of substance use, externalizing symptoms, and internalizing symptoms were gathered, typically from multiple reporters. Multilevel modeling revealed that greater levels of romantic involvement in adolescence were associated with higher levels of substance use and externalizing symptoms but became associated with lower levels in adulthood. Having a romantic partner was associated with greater levels of substance use, externalizing symptoms, and internalizing symptoms in adolescence but was associated with lower levels in young adulthood. The findings were not consistent with a social timetable theory, which predicts that nonnormative involvement is associated with poor adjustment. Instead, the findings are consistent with a developmental task theory, which predicts that precocious romantic involvement undermines development and adaptation, but when romantic involvement becomes a salient developmental task in adulthood, it is associated with positive adjustment. Discussion focuses on the processes that may underlie the changing nature of the association between romantic involvement and adjustment.