Predrinking (or pregaming) is common among undergraduates and has been linked with problem alcohol use. While many students predrink to save money, evidence suggests that some students predrink to cope with social anxiety (SA). Tension reduction and cognitive theories predict that those high in SA may predrink to reduce anticipatory anxiety before attending social events and their predrinking may be done alone rather than in normative social contexts. Available data suggest that, relative to social drinking, solitary drinking elevates risk for alcohol use and related problems. Informed by this evidence, we speculated that context for predrinking may be an important mechanism by which SA-risk for alcohol use unfolds. Specifically, we offered the novel hypothesis that those high in SA would engage frequently in solitary predrinking and this in turn would be associated with elevated alcohol use and related problems. Undergraduate drinkers (N = 293; 70% women) completed self-reports of social anxiety, predrinking context (social, solitary), alcohol use, and alcohol-related problems. In partial support of our hypotheses, SA was a positive predictor of solitary predrinking, which in turn predicted elevated alcohol-related problems, but not alcohol use. While not hypothesized, we also found that SA was a negative predictor of social predrinking, which in turn reduced risk for alcohol use and related problems. Our study is the first in the literature to show that solitary predrinking helps explain the well-documented association between SA and alcohol-related problems. These findings may inform etiological models and clinical interventions, suggesting that SA-risk for problem drinking begins even before the party starts.