Parents’ knowledge of their adolescents’ whereabouts and activities is a robust predictor of adolescent risk behavior, including the use of drugs and alcohol. Surprisingly few studies have attempted to identify parental characteristics that are associated with the degree of parental knowledge. The present study is the first to examine how parental attachment style relates to mother, father, and adolescent reports of parental knowledge. Further, we used structural equation modeling to test the associations among parents’ attachment styles, reports of parental knowledge, and adolescents’ alcohol and marijuana use. Participants included 203 adolescents (M age = 14.02, SD = .91) living in 2-parent households and their parent(s). As predicted, mothers’ and fathers’ insecure attachment styles were negatively associated with self-reported and adolescent-reported parental knowledge, and all 3 reports of parental knowledge were negatively related to adolescent substance use. Mothers’ and fathers’ attachment styles were unrelated to adolescent substance use. However, evidence emerged for indirect effects of parental attachment style on adolescent substance use through reports of parental knowledge. Implications for prevention efforts and the importance of multiple reporters within the family are discussed.