This study utilized data drawn from a study of 980 adolescents living in Tijuana, Mexico, in February 2009 to examine whether parental monitoring had a moderating impact on the influence of peer pro-drug norms on lifetime and past-30-day alcohol and cigarette use among a group of adolescents living along the United States-Mexico border. The results of primary analyses indicated that parental monitoring did moderate the influence of peer pro-drug norms for past-30-day cigarette use for males but not for females. Research and practice implications for U.S. and Mexican culturally grounded prevention programs are discussed.