The goals of this study were to examine associations between within- and between-person social risk and victimization and cannabis use among emerging adults in substance-use treatment. We also tested gender differences for both victimization and social risk. Participants consisted of 3,052 emerging adults (Mage = 20.0 years; SD = 2.21) entering substance-use treatment in a wide range of treatment centers across the United States. Individuals were assessed on all measures at baseline 3, 6, and 12 months. We fitted a taxonomy of multilevel growth curve models to test main effects, and interactive relations between within- and between-person social risk, victimization, and gender on cannabis use. Several significant interactions were evident. Irrespective of gender, within-person increases in social risk were associated with contemporaneous increases in cannabis use; however, the magnitude of this relation was comparatively more pronounced for men. Similar gender differences emerged between individuals. Males experiencing heightened social risk over time tended to show high levels of early cannabis use. Simple slope analyses revealed that reporting more (+1 SD) social risk than one’s own mean resulted in significant increases in cannabis use for both men and women. Cross-level simple slope analyses revealed no differences in cannabis use among individuals reporting low (−1 SD) social risk and victimization, but significant increases in cannabis use for individuals reporting high (+ 1 SD) victimization and social risk. Results demonstrate support for gender differences in social risk on cannabis use and the importance of considering within-person effects.