The United States Surgeon General and the National Institute of Mental Health have focused attention on discovering the early risk factors in the development of sexual aggression in order to target prevention programming. In response to this call for research, the current study examined developmental pathways leading to the expression of sexual aggression and delinquent behavior in youths, with a focus on the effects of exposure to violence against women and male-modeled antisocial behavior. Participants were 182 adolescent male sex offenders recruited from multiple public and private institutional treatment programs for juvenile sex offenders. Sexual offense data were taken from institutional records and participants completed a social history questionnaire that elicited information about developmental experiences and engagement in nonsexual aggression and delinquency. Personality constructs and delinquent attitudes were also assessed using a battery of assessment instruments. Results of structural equation modeling indicated that both childhood exposure to violence against women and male-modeled antisocial behavior produced direct and indirect effects on nonsexual aggression and delinquency; important mediating roles were played by Psychosocial Deficits and Egotistical-Antagonistic Masculinity. In particular, Psychosocial Deficits mediated the relationship between exposure to violence against women and engagement in sexual aggression. Findings supported the hypothesis that youths who sexually offend against prepubescent children expressed greater deficits in psychosocial functioning, committed fewer offenses against strangers, and expressed less violence in their sexual offending than youth who sexually offend against pubescent females. Two major evolutionary psychological concepts, intrasexual selection and intersexual selection, are explored in terms of their explanatory power concerning human sexual behavior. Future research should continue to explore various risk and protective factors for the development of sexual aggression. Tables, figure, references