The predictors of cessation of marijuana and cocaine use were examined in a longitudinal cohort of young adult men and women (N = 1222). Six domains of predictors were examined: socioeconomic background variables, participation in the social roles of adulthood, degree of drug involvement, social context of drug use, health status, and deviant activities and conventionality of life experiences. Factors that predicted cessation of use in adulthood paralleled those that predicted lack of initiation in adolescence: conventionality in social role performance, social context unfavorable to the use of drugs, and good health. A most important predictor was prior degree of involvement in licit and illicit drugs. In multivariate analyses, degree of prior drug involvement remained the strongest predictor of drug cessation for of marijuana use, while friends' use was the most important for cocaine. Those who use drugs in response to social influences are more likely to stop using them than those who also use drugs for psychological reasons.