Background and aims Emerging evidence suggests that solitary drinking may be an important early risk marker for alcohol use disorder. The current paper is the first meta‐analysis and systematic review on adolescent and young adult solitary drinking to examine associations between solitary drinking and increased alcohol consumption, alcohol problems, and drinking to cope motives. Methods PsychINFO, PubMed, and Google Scholar were searched using the Preferred Reporting Items for Systematic Reviews and Meta‐Analyses (PRISMA) methodology and a pre‐registered International Prospective Register of Systematic Reviews (PROSPERO) protocol (no. CRD42020143449). Data from self‐report questionnaires regarding negative correlates of solitary drinking (e.g. alcohol problems) and solitary drinking motives (e.g. drinking to cope) were pooled across studies using random‐effects models. Studies included adolescents (aged 12–18 years) and young adults (mean age between 18 and 30 years or samples with the majority of participants aged 30 years or younger). Results Meta‐analytical results from 21 unique samples including 28,372 participants showed significant effects for the associations between solitary drinking and the following factors: increased alcohol consumption, r = 0.23, 95% confidence interval (CI) = 0.12, 0.33; drinking problems, r = 0.23, 95% CI = 0.13, 0.32; negative affect, r = 0.21, 95% CI = 0.16, 0.26; social discomfort, r = 0.17, 95% CI = 0.06, 0.27; negative reinforcement, r = 0.28, 95% CI = 0.24, 0.31; and positive reinforcement, r = 0.10, 95% CI = 0.03, 0.17. These associations were not moderated by age group (i.e. adolescent versus young adult), study quality, or differing solitary drinking definitions. Accounting for publication bias increased the effect sizes from r = 0.23 to 0.34 for alcohol consumption and from r = 0.23 to 0.30 for drinking problems, and lowered it from r = 0.10 to 0.06 and r = 0.17 to 0.11 for positive reinforcement and social discomfort, respectively. Conclusions Solitary drinking among adolescents and young adults appears to be associated with psychosocial/alcohol problems and drinking to cope motives.