Personality disorders are highly comorbid with major depression; however, findings are mixed regarding their impact on depression treatment outcomes and trajectories. Limited research has studied personality pathology in winter depression, specifically. This study (1) explored the prevalence of personality pathology in winter depression and (2) examined its effects on winter depression treatment trajectories. Participants were 174 adults with Major Depression, Recurrent with Seasonal Pattern from a randomized clinical trial comparing group cognitive-behavioral therapy for seasonal affective disorder (CBT-SAD) and light therapy. Participants completed the Millon Clinical Multiaxial Inventory-III (MCMI-III; Millon et al., 1994) at baseline. The prevalence of MCMI-III-defined pathological personality traits and personality disorders in this sample was 98/174 (56.3%) with any trait and 65/174 (37.4%) with any disorder. Dependent was the most common elevation (65/174, 37.4%), trait (43/174, 24.7%), and disorder (22/174, 12.6%). Most participants with pathological personality elevations had only one personality disorder (58/174, 33.3%) and one pathological personality trait (82/174, 47.1%). Growth curve analysis revealed personality pathology predicted higher baseline depression scores, but the number of MCMI-III pathological personality elevations (i.e., traits and disorders) and personality disorders did not predict change in depression over the timeframe of pretreatment, weekly during treatment, posttreatment, and follow-ups one and two winters later in CBT-SAD or light therapy. Results suggest that personality pathology is not a negative prognostic indicator or prescriptive factor for winter depression treatment with CBT-SAD or light therapy, which may inform treatment algorithms and decision-making in practice.