Background: Attachment theory's original formulation was substantially driven by Bowlby's (1969/1982) quest for a meaningful model of the development of psychopathology. Bowlby posited that aberrant experiences of parenting increase the child's risk of psychopathological outcomes, and that these risks are mediated by the quality of the attachment relationship. To empirically examine this hypothesis, the current study explores the associations between the development of toddler behavior problems and a) maternal unresolved attachment representations, b) maternal interactive behavior, and c) infant attachment relationships. Second, we test the mediating role of disorganized attachment in the association between disruptive behavior and toddler behavior problems, as well as unresolved attachment and behavior problems. Method: Sixty-four adolescent mother-infant dyads participated in this longitudinal study. The Adult Attachment Interview was administered at 6 months, the Strange Situation procedure was conducted at 12 months, disrupted behavior was assessed during play interactions at 12 months using the AMBIANCE measure, and the Child Behavior Checklist (CBCL) was used to assess behavior problems at 24 months of age. Results: Maternal reports of externalizing problems were significantly associated with unresolved representations of attachment, disrupted maternal behavior, and disorganized attachment. Inclusion of these variables in a path analytic model suggested that disorganized attachment mediated the associations between disrupted maternal behavior and externalizing problems. Although the association between unresolved attachment representations and externalizing problems was no longer significant when mediation by disrupted behavior and disorganized attachment was taken into account, this indirect pathway was not significant. Conclusions: The results are consistent with Bowlby's (1969/1982) original conceptualization of the explanatory role of the attachment relationship in the development and manifestation of behavioral maladaptation. Effects of unresolved attachment on externalizing problems await further explanation. © 2007 The Authors.