Striking differences appeared among 1,325 young adults aged 24 to 25 years depending on their marijuana use. Differences increased with involvement, although no threshold appeared at any particular level. Marijuana users were characterized by higher use of other substances, membership in networks of marijuana users, lower participation and greater instability in conventional roles of adulthood, history of psychiatric hospitalization and lower psychological well-being, and participation in deviant activities. Involvement with marijuana-using friends and use by spouse or partner, as well as use of other illicit drugs, were important predictors of current marijuana involvement. In young adulthood, as in adolescence, marijuana use is embedded in a social context favorable to its use and is associated with disaffection from social institutions. The social and psychological correlates of marijuana use are similar in young adulthood and adolescence and have remained unchanged over the last decade.