Although the majority of adopted children are well-adjusted, adopted children evidence proportionately more behavior problems when compared to nonadopted children in both clinic and nonclinic populations. An extensive literature examining behavioral, diagnostic, and demographic characteristics of adopted children has provided several plausible explanations for the high rate of behavior problems among adopted children. In this review, the existing literature is organized into five explanatory models: (a) genetic or "biosocial" factors, (b) pathogenesis of the adoption process, (c) long-term effects of impaired preadoption childrearing, (d) referral bias in adoptive parents, and (e) impaired adoptive parent-adoptee relations. We conclude that evidence for each model is mixed at best. Especially noteworthy is the mixed results for genetic or biosocial studies and the relative absence of studies focused on identifying factors associated with disruptions in the adoptive parent-adoptee relationship. We propose that a psychosocial model to explain the high rate of behavior problems among adopted children is highly plausible and further suggest that it may be time for a new awareness and appreciation for the normative aspects of adoption. An overview of parenting and family characteristics associated with risk factors for antisocial behavior is provided as a guide for future research.