A substantial body of research points to several variables relevant to the etiology of borderline personality disorder (BPD), notably childhood physical and sexual abuse, childhood family environment, and familial aggregation of both internalizing and externalizing disorders. However, these variables tend to be correlated, and few studies have examined them simultaneously. A national sample of randomly selected psychologists and psychiatrists described 524 adult patients with personality disorders. Family environment, parental psychopathology, and history of abuse all independently predicted BPD symptoms in multiple regression analyses. Sexual abuse contributed to the prediction of BPD symptoms over and above family environment, although family environmental factors such as instability partially mediated the effect. The results converge with recent studies using very different samples and methodologies.