Objective: To evaluate the efficacy, safety, and tolerability of oxcarbazepine (1,200 mg/day) vs placebo as prophylactic therapy for patients with migraine headaches. Methods: This multicenter, double-blind, randomized, placebo-controlled, parallel-group trial consisted of a 4-week single-blind baseline phase and a 15-week double-blind phase consisting of a 6-week titration period, an 8-week maintenance period, and a 1-week down-titration period, after which patients could enter a 13-week open-label extension phase. During the 6-week titration period, oxcarbazepine was initiated at 150mg/day and increased by 150mg/day every 5 days to a maximum tolerated dose of 1,200 mg/day. The primary outcome measure was change from baseline in the number of migraine attacks during the last 28-day period of the double-blind phase. Results: Eighty-five patients were randomized to receive oxcarbazepine and 85 to receive placebo. There was no difference between the oxcarbazepine (- 1.30) and placebo groups in mean change in number of migraine attacks from baseline during the last 28 days of double-blind phase (-1.74; p = 0.2274). Adverse events were reported for 68 oxcarbazepine-treated patients (80%) and 55 placebo-treated patients (65%). The majority of adverse events were mild or moderate in severity. The most common adverse events (>= 15% of patients) in the oxcarbazepine-treated group were fatigue (20.0%), dizziness (17.6%), and nausea (16.5%); no adverse event occurred in more than 15% of the placebo-treated patients. Conclusions: Overall, oxcarbazepine was safe and well tolerated; however, oxcarbazepine did not show efficacy in the prophylactic treatment of migraine headaches.