The current study tested sex-specific pathways to early puberty, sexual debut, and sexual risk taking, as specified by an integrated evolutionary-developmental model of adolescent sexual development and behavior. In a prospective study of 238 adolescents (n = 129 girls and n = 109 boys) followed from approximately 12-18 years of age, we tested for longitudinal relations between ecological stressors, family relationships, pubertal maturation, self-perceived mate value, and sexual risk taking in both boys and girls. Consistent with the theory, (a) higher levels of familial and ecological stress predicted earlier sexual debut and greater sexual risk taking; (b) pubertal maturation partially mediated these relations among girls but not among boys; (c) father absence had unique effects on female sexual outcomes but not on male sexual outcomes; (d) higher self-perceived mate value directly predicted earlier sexual debut and, through it, greater sexual risk taking; and (e) relations between pubertal maturation and early sexual debut were partially mediated by higher self-perceived mate value in boys but not in girls. Discussion focuses on the contribution of an integrated evolutionary-developmental theory to the adolescent sexual health literature. (Contains 3 tables, 2 footnotes and 2 figures.)