Objective: Although adolescent alcohol use has been consistently associated with parental drinking behavior, sibling drinking behavior and family functioning, the extent to which these associations owe to genetic or shared environmental influences has not been previously investigated. Using an adoption study design, we sought to determine whether the familial correlates of adolescent alcohol involvement were due to common genetic or common environmental effects. Method: The sample consisted of 653 adopted families ascertained through adoption agencies in four U.S. states. Each family consisted of a target adopted adolescent, an adoptive mother and an adoptive father. In addition, 68 both adolescents (i.e., biological offspring of the adoptive parents) and 187 second adopted adolescents from these families participated in the study. All participants completed a mail survey that included assessment of drinking behavior and family functioning. Results: The relationship between parental problem drinking and adolescent alcohol involvement was moderate and significant among birth offspring (corrected multiple correlation, R(r) = .30), but small and non-significant among adoptive offspring (R(r) = .00). The relationship between adolescent alcohol involvement and family functioning was substantial for both offspring (R(c) = .39), but only modest for adoptive offspring (R(c) = .16). The nonbiological sibling correlation for involvement with alcohol was significant (r = .24) and moderated by sibling pair demographic similarly, such that same sex, similar-age siblings were substantially more similar (r = .45) than opposite-sex, dissimilar aged siblings (r = .01). Conclusions: These findings suggest that adolescent alcohol use is affected minimally by the environmental consequences of parent problem drinking and family functioning, but substantially by sibling environmental effects.