Although antisocial personality disorder (ASPD) is more common among males and borderline PD (BPD) is more common among females, some authors have suggested that the two disorders reflect multifinal outcomes of a single etiology. This assertion is based on several overlapping symptoms and features, including trait impulsivity, emotional lability, high rates of depression and suicide, and a high likelihood of childhood abuse and/or neglect. Furthermore, rates of ASPD are elevated in the first degree relatives of those with BPD, and concurrent comorbidity rates for the two disorders are high. In this article, we present a common model of antisocial and borderline personality development. We begin by reviewing issues and problems with diagnosing and studying PDs in children and adolescents. Next, we discuss dopaminergic and serotonergic mechanisms of trait impulsivity as predisposing vulnerabilities to ASPD and BPD. Finally, we extend shared risk models for ASPD and BPD by specifying genetic loci that may confer differential vulnerability to impulsive aggression and mood dysregulation among males and impulsive self-injury and mood dysregulation among females. Although the precise mechanisms of these sex-moderated genetic vulnerabilities remain poorly understood, they appear to interact with environmental risk factors including adverse rearing environments to potentiate the development of ASPD and BPD.