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Background: A number of important sociological, psychological, and biological predictors of adolescent criminal behavior have been identified during the most recent decades. The aim of this study was to replicate recent findings that interactions between a polymorphism in the monoamine oxidase A (MAO-A) gene promoter region and psychosocial factors might predict male adolescent criminal activity. Methods: A cross-sectional study with a randomized sample from the total population of 16- and 19-year-olds from the county of Vastmanland, Sweden. Eighty-one male adolescents, who volunteered to participate, were randomly selected from groups representing different degrees of deviant risk behavior. Results: The present study strongly supports the notion that carrying the 3-repeat allele of the MAO-A- gene promoter increases the risk of male adolescent criminal behavior, when interacting with psychosocial factors. No effects at all of the MAO-A genotype on adolescent criminal activity were found when MAO-A genotype was considered alone (i.e., without its psychosocial context). The explained variance of the bio-psychosocial model (controlling for MAO-A) in this study exceeded the psychosocial model by 12%. Conclusions. The findings support the notion that genotype and psychosocial factors interact to precipitate male adolescent criminal behavior.