The influence of friend substance use on the association between pubertal timing and substance use has received little consideration in the literature. With a sample of 264 female adolescents (11–17 years), this study examined (a) the relationship between pubertal timing and substance use, (b) the impact of number of friends that smoke cigarettes on adolescents' use of three substances (cigarettes, alcohol, and marijuana), and (c) the interactions between pubertal timing and friends' smoking in predicting individual substance use. Results showed a significant relationship between pubertal timing and alcohol use; later timing was related to more alcohol use. This association between late timing and alcohol use is contrary to previous literature and may be due to the broad age range of this sample. Pubertal timing may have less of an effect in late adolescence when drinking becomes more normative and less deviant; the rationale for this association is discussed. Second, this study found females who reported that more of their friends smoke regularly (at least once a week) used significantly more cigarettes, alcohol, and marijuana than those who reported no friends who smoke. Finally, the interaction between pubertal timing and number of friends who were regular smokers was not significantly related to adolescent substance use. However, friend smoking explained more of the variation in substance use than pubertal timing. This indicates that having friends who smoke is more influential in predicting substance use than pubertal timing. These findings are important when considering the development of interventions to target adolescent substance use.