Early risk factors for gambling participation (GP) and substance use (SU) in adolescents have usually been studied separately, although these disorders were integrated into the same clinical category over a decade ago. This exploratory study aimed to investigate the early individual, parental, familial and social risk factors associated with developmental patterns of adolescent GP and SU in a population-representative cohort (N = 1594, 51.2% boys). Using a person-centered strategy and multiple assessments from age 12 to 17, six developmental patterns describing joint GP and SU courses were revealed. Non-substance users/non-gamblers served as the reference class in an integrated longitudinal-multivariate analysis framework examining 15 distinct risk factors. Results showed that a core of risk factors were common to all trajectory-classes of substance users with or without GP. For a similar level of SU, most of the risk factors associated with non-gambling users also affected their gambling peers. However, additional risk factors were specifically related to GP. Thus, substance users who also gamble were affected by a greater number of risk factors than non-gambling substance users. Findings are consistent with a developmental syndrome of addiction, which posits a shared etiology between different expressions of addiction as well as differences in risk factors that lead to distinct trajectories of addictive behaviors. They highlight the importance of considering both GP and SU for a comprehensive assessment of adolescents' level of risk with regard to addictive behaviors. [Author's abstract]