Background: Time-varying associations of 185 at-risk men’s (from the Oregon Youth Study) substance use with that of their peers and partner over a 10-year period (ages 23-32 years) were examined. Moderation of effects by time with peers and partner and age were tested. Method: Growth models were used to predict changes in heavy episodic drinking (HED), any alcohol use and marijuana use as a function of substance use by their female partner and male peers. Results: Time with peers and peer substance use significantly predicted HED (ORs=1.6, 2.3), alcohol use (ORs=1.6, 2.1), volume of alcohol use (IRRs=1.5, 1.3), marijuana use (ORs=12.8, 1.7), and peer marijuana use predicted volume of marijuana use (B=2.5). Partner substance use significantly predicated marijuana volume (B=2.7). Partner alcohol use predicted alcohol volume (IRR=1.1), but was moderated by time with parent and age (IRR=1.0). Time with partner and partner marijuana use predicted marijuana use (OR=0.5, 2.7), as did the interaction of the two (OR=3.8). Conclusions: Outcome-specific substance use of peers and partners is significantly associated with indicators of alcohol and marijuana use in men’s early adulthood, with robust effects of peer substance use through age 30, and with time spent with peers influencing alcohol use. Time with partner was protective against marijuana use unless the partner used marijuana. Interventions related to associations with substance using peers and couple treatment for substance use may be effective in early adulthood for men.