Laboratory research in adults indicates that alcohol-related subjective effects are enhanced under some social conditions. However, it is unknown whether this "social facilitation" of alcohol effects occurs in adolescents and is associated with alcohol use in the natural ecology.We examined associations of social facilitation of alcohol-related subjective effects with subsequent alcohol use among a relatively high-risk group of adolescents who reported drinking alcohol both with friends and alone.Los Angeles high school students from a prospective study (N = 142; 51% female; 10th graders) completed a baseline survey that assessed alcohol-related "positive" and "negative" subjective effects in two contexts: social (alcohol with friends) and solitary (alcohol alone); social facilitation was calculated as the difference between social and solitary. Students then completed five semi-annual surveys spanning 30 months (2014-2017) assessing 30-day alcohol use (days used, number of drinks, binge drinking).Greater social facilitation of positive effects was significantly associated with greater number of alcohol use days (RR [95% CI] = 1.48 [1.19, 1.82]; p < .001), greater number of drinks (RR [95% CI] = 1.38 [1.14, 1.66]; p = .001), and greater odds of binge drinking (OR [95% CI] = 1.75 [1.20, 2.57]; p = .004). Similar associations were found with social positive effects. There were no significant associations between solitary positive effects-or any negative effects-and alcohol use outcomes.Social facilitation can be measured outside of the laboratory. Relatively high-risk drinking adolescents who are more susceptible to the social facilitation of subjective alcohol effects are more likely to use more alcohol and binge drink.