Sociological and criminological studies have established the influence of family and peers on adolescent deviance. Studies have focused on the relative influence of parent rearing practices, family structure, social class, and genetics on delinquency. Overlooked by these previous studies is an examination of the behavioral influence of siblings on an adolescents’ propensity to engage in deviance. This study drew on data from the 1995-1996 National Longitudinal Study of Adolescent Health (Add Health), which questioned a nationally representative sample of adolescents in grades 7 through 12 from randomly selected schools throughout the United States. Respondents were asked about their close friends, aspects about their family structure and relationships, and participation in deviant activities. The authors matched and extrapolated a final sample of 1,015 sibling pairs for examination; 135 of the sibling pairs were identical twins, 187 were fraternal twins, and 693 were full-sibling pairs. Measures of deviance included smoking cigarettes, drinking, skipping school, and fighting. The quality of the relationship between siblings and parents and respondents was measured through questions on closeness, parental supervision, parent-child autonomy, and parental conflict. In the analysis, genetic relatedness was controlled for using DeFries-Fulker regression. Results of multivariate analyses indicate that when shared and non-shared environmental aspects were controlled, the heritability effect was not significantly related to adolescent deviance. The influence from unique friends was the most significant predictor of adolescent deviance, net of background control variables. The authors speculate that unique friends offer an adolescent the greatest autonomy in terms of who they select for friendships. As such, bonds to unique friends may be stronger than bonds to friends shared by both siblings (mutual friends), resulting in greater vulnerability to peer pressure by unique friends. Future research should focus on whether school or community factors moderate the influence of sibling and peer deviance on engagement in deviance. Tables, references