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Both peer groups and genetics have been associated with adolescent smoking behavior. Recently, Loehlin (Loehlin, J. C. (2010). Is there an active gene–environment correlation in adolescent drinking behavior?Behavior Genetics, 40, 447–451) reported that twin differences in alcohol use were associated with differences in the number of common friends. Twins with more common friends were more similar in drinking, but only for dizygotic pairs. Using the same sample as Loehlin's (the National Merit twins), we replicated all of these findings for a composite cigarette smoking measure and for smoking initiation, but not persistence. The pattern of results is most consistent with homophily, or the tendency to associate with individuals that are like oneself. If peer influence occurs in the presence of homophily, then active genotype–environment correlation will be induced.