The present study tested the hypothesis that teens who engage in conduct problems are more likely to use substances because they engage in fewer alternative reinforcing (i.e., pleasurable) substance-free activities and more complementary reinforcing substance-associated activities. In a cross-sectional, correlational design, 9th grade students (N = 3,383; mean age = 14.6 years) in Los Angeles, California, U.S.A. completed surveys in 2013 measuring conduct problems (e.g., stealing, lying, getting in fights); alternative and complementary reinforcement; use of a number of licit, illicit, and prescription drugs; and other cofactors. Conduct problems were positively associated with past 6-month use of any substance (yes/no) among the overall sample and past 30-day use frequency on a composite index that included 6 substances among past 6-month users. These associations were statistically mediated by diminished alternative reinforcement and increased complementary reinforcement when adjusting for relevant covariates. Conduct problems were associated with lower engagement in alternative reinforcers and increased engagement in complementary reinforcers, which, in turn, were associated with greater likelihood and frequency of substance use. Most mediational relations persisted adjusting for demographic, environmental, and intrapersonal cofactors and generalized to alcohol, cigarette, and marijuana use, although, complementary reinforcers did not significantly mediate the relation of conduct problems with alcohol use frequency. These results point to diminished alternative reinforcement and increased complementary reinforcement as mechanisms linking conduct problems and adolescent substance use. Interventions that increase access to and engagement in a diverse set of alternative substance-free activities and deter activities that complement use may prevent substance use in adolescents who engage in conduct problems.