The efficacy and tolerability of cinnarizine (75 mg, at bedtime) in migraine prophylaxis and the presence of possible predictive factors for therapeutic responsiveness were evaluated in an open-label pilot trial. Eighty consecutive outpatients suffering from migraine with or without aura participated in the study. After 12 weeks of therapy, 55 patients experienced a greater than 66% reduction in headache frequency and were considered responders. A significant reduction in the number of migraine days (mean reduction 58 +/- 8%) and in intake of medication to treat acute attacks (mean reduction 55 +/- 11%) was also observed. Cinnarizine was well tolerated, as documented by the low number of adverse effects. Failure to respond to previous prophylactic treatments was a negative predictive factor correlated with a poor prognosis. This study, even bearing in mind its limitations as an open-label trial, suggests that cinnarizine might be an effective prophylactic anti-migraine agent. The clinical characteristics of migraine patients do not help to predict response to treatment.