Outcome after 6 days of morning light therapy in subjects fulfilling criteria for winter seasonal affective disorder (SAD) was examined. Responders had significantly fewer previous episodes of SAD. Patients with a diagnosis of any DSM-III-R, axis II personality disorder, were significantly less likely to respond to light therapy than patients without axis II pathology. Poor treatment outcome was also significantly associated with: one or more personality disorders in cluster C, avoidant personality disorder, high number of positive criteria for self-defeating personality disorder and high score on the harm avoidance scale of the Tridimensional Personality Questionnaire. Temperament accounted for 25% of the variance in treatment outcome.