An 8-month, double-blind, placebo-controlled, crossover trial of flunarizine in the prophylaxis of migraine has been performed in 70 children. After 4 weeks of medication-free base-line observation, 35 children (group A) received flunarizine (5 mg/day) and 35 (group B) received placebo over a 12-week period. After a 4-week washout they crossed treatments for another 12 weeks. Sixty-three patients completed the trial. In both groups flunarizine significantly reduced the frequency and average duration of headache attacks. In group A efficacy was maintained after placebo crossover for the last 4 months of the study. Five subjects in group B stopped placebo because of ineffectiveness; two children in group A discontinued flunarizine treatment, one because of excessive daytime sedation and the other because therapy was ineffective. The main side effects were daytime sedation and weight gain. It is concluded that flunarizine is an effective drug for the treatment of childhood migraine. In a study of this length no serious side effects were discovered.