Hazardous drinking in emerging adulthood is associated with multiple domains of alcohol problems, which range in type and severity. Alcohol problems at the severe end of the spectrum (e.g., impaired control) may be early warning signs of alcohol use disorders (AUDs) among emerging adults. However, given the emphasis in the literature on predictors of overall problem risk, we still know very little about predictors of these specific (and severe) domains of alcohol problems in emerging adults. Many emerging adults drink at social events (e.g., parties), but an estimated 15% engage in solitary drinking. Solitary drinking – a developmentally atypical behavior in emerging adulthood – may be especially risky. Data suggests that frequent solitary drinking may reflect a loss of control over drinking, leading to hazardous use and subsequent problems. Accordingly, we expected that frequent solitary drinking among emerging adults would predict severe alcohol problems that map onto diagnostic criteria for AUDs and these effects would be mediated by hazardous alcohol use. Undergraduates (N = 118) completed self-report measures as a part of a larger study on motivation and alcohol use. As predicted, path analysis showed that solitary drinking positively predicted hazardous alcohol use, and this in turn predicted severe alcohol problems associated with diagnostic criteria for AUDs, particularly risky behaviors and blackout drinking. Solitary drinking also positively predicted less severe problems of diminished self-perception and poor self-care through hazardous use. Though comparatively smaller, some indirect effects were observed from social drinking (at parties, but not at bars) to alcohol problems, via hazardous alcohol use. Overall, our results suggest that solitary drinking is particularly harmful in emerging adulthood.