BACKGROUND Patients with social phobia often describe personality traits characterized by avoidant social behavior and more general depressive-anxious features. There is only sparse knowledge about the effects of drug treatment on these traits. METHODS Fifty-seven patients with social phobia completed a 12-week double-blind, placebo-controlled trial with the reversible and selective monoamine oxidase A inhibitor brofaromine 150 mg/day. The Clinical Global Impressions-Improvement scale, Liebowitz Social Anxiety Scale, a questionnaire with 140 items regarding personality traits, and ratings on the presence or absence of diagnostic criteria for the DSM-III-R avoidant and dependent personality disorders were used for assessments at baseline and endpoint. Comparisons were made with a group of 58 healthy controls. RESULTS Before treatment, there were no significant differences between the brofaromine and placebo groups in their ratings on situationally bound social anxiety or on personality traits that differed significantly from those of the controls. At endpoint, a marked normalization was noted in the brofaromine group. The changes that had occurred differed significantly from those in the placebo group. The normalization of traits seemed more marked than the normalization of anxiety in more specific social phobic situations. The number of brofaromine patients who fulfilled the criteria for avoidant personality disorder had diminished from 15 (60%) to 5 (20%). CONCLUSIONS The results support the conclusion that the maladaptive personality traits characteristic of social phobia are at least as responsive to the monoamine oxidase inhibitor brofaromine as are the more circumscribed social anxiety responses.