The aim of the study described here was to investigate the efficacy, tolerability, and side effects of oxcarbazepine (OXC) monotherapy in newly diagnosed, previously untreated adult and elderly patients with partial epilepsy. We prospectively analyzed and recorded the efficacy, tolerability, and side effects of OXC monotherapy. The results were analyzed on the basis of etiologic classifications and age distributions. Remission was defined as seizure freedom for at least 1 year. A total of 147 patients were evaluated in a single center for a median of 18 months (range: 14-36 months). Overall, 92 patients (62.6%) were seizure free for at least 12 months and 55 of them (37.4%) were unresponsive despite treatment with the maximum tolerable dose of OXC. There was a significant difference in the outcomes of patients with cryptogenic (75% remission) and symptomatic (51.9% remission) epilepsy (P=0.004). Patients with cerebral tumors did worse than the remainder of the patients in the symptomatic group (36.7% remission) (P=0.03). Results were favorable for the elderly; 14 patients (73.6%) in the elderly subgroup became seizure free for at least 1 year, and the remission was achieved with low to moderate doses (approximately 900 mg/day). Overall, 13 patients (8.8%) discontinued OXC due to intolerable side effects. Side effects leading to discontinuation were: Stevens-Johnson syndrome (n=2, 1.4%); fatigue and drowsiness (n=2, 1.4%); dizziness, nausea, and vomiting with normal laboratory tests (n=2, 1.4%); dizziness, nausea, and vomiting with serum Na levels <130 mEq/L (n=5, 3.4%); and elevated serum gamma-glutamyl transferase levels (GGT>200mg/dL) (n=1, 0.7%). OXC proved to be a tolerable drug for the elderly; only one patient experienced symptomatic hyponatremia with mild symptoms and responded well to fluid restriction, which did not lead to discontinuation of OXC. Although the limitations of our study include its open-label design, the results suggest that OXC monotherapy may be regarded as an effective first-line monotherapy option for adult and elderly patients with partial epilepsy, but has low efficacy in patients with cerebral tumors.