AimsThis study estimated the extent of familial alcohol supply in 45 low and middle income countries (LMIC), and examined the country-level effects of familial alcohol supply on adolescents’ alcohol use. MethodWe used data from 45 LMICs that participated in the Global School-Based Student Health Survey (GSHS) between 2003 and 2013 (n = 139,840). The weighted prevalence of familial alcohol supply in each country was estimated. Multilevel binary and ordinal logistic regression analyses were used to examine the country-level effect of familial alcohol supply on early onset of alcohol use (first alcohol before 12), past 30-day alcohol use, lifetime drunkenness and alcohol-related social problems. ResultsThere were large variations between LMICs in the prevalence of familial alcohol supply and pattern of adolescent alcohol use. The prevalence of familial supply ranged from 0.1% in Tajikistan to 23.8% in St Lucia. It was estimated that a one percentage change in prevalence of familial alcohol supply was associated with 10%, 12% and 12% change in the odds of lifetime drunkenness (OR = 1.10, 95% CI = [1.04, 1.16]), early onset of alcohol use (OR = 1.12, 95% CI = [1.07, 1.08]) and more frequent drinking in the past month (OR = 1.12, 95% CI = [1.04, 1.20]). ConclusionThere were large variations in the prevalence of familial alcohol supply and adolescent alcohol use among LMICs. Adolescents in countries with higher prevalence of familial alcohol supply were more likely to start using alcohol at an earlier age, to have used alcohol in the past 30 days and experience intoxication.