This study prospectively examined whether continued add-on treatment with oxcarbazepine (OXC) is associated with quantitative improvement in mood and anxiety symptoms in adult patients with partial epilepsy. Depressive symptoms and anxiety were assessed by clinical interview using the Hamilton Depression Rating Scale (HDRS), the Cornell Dysthymia Rating Scale (CDRS), the Beck Depression Inventory (BDI), and the Hamilton Anxiety Rating Scale (HARS). Forty controls (patients with epilepsy treated with antiepileptic drugs other than OXC) and 40 OXC-treated patients were enrolled and completed the study. In our study, a significant improvement in affect, as measured by the CDRS, was demonstrated during the course of OXC treatment for 3 months. HDRS and BDI scores also declined in the OXC-treated group, but these decreases did not reach statistical significance. In addition, 28 of 40 OXC-treated subjects who were dysthymic by CDRS criteria on study entry (score > or =20) demonstrated affective improvement consistent with a treatment-related antidepressant effect (score <20). Although our results do not provide conclusive evidence supporting the specific use of OXC as an antidepressant, the significant decline in dysthymic symptoms in OXC-treated subjects compared with controls lends support to the hypothesis that OXC improves mood.