This multicenter, double-blind, clinical study was designed to compare the efficacy and safety of alpha-dihydroergocryptine and flunarizine in the prophylaxis of migraine without aura. One hundred thirty-five patients fulfilling the diagnostic criteria of the International Headache Society were enrolled at five neurologic centers. The study design included a 1-month pretreatment phase with placebo; a 6-month, double-blind, double-dummy treatment phase with alpha-dihydroergocryptine (10 mg twice daily) or flunarizine (5 mg once daily); a further 3-month follow-up phase without treatment. Efficacy was assessed using the patient's diary. Laboratory tests, vital signs, and adverse events were monitored. Analysis of covariance for repeated measures was performed on the intent-to-treat sample. Both treatments led to a significant reduction in the frequency of migraine, days with headache, and use of relief medication. Overall, 51% of those treated with alpha-dihydroergocryptine and 49% of those treated with flunarizine were responders (50% or greater reduction in attack frequency), the average percentage of reduction being 64% with alpha-dihydroergocryptine and 51% with flunarizine. There was no significant difference between the two groups in terms of incidence of adverse events; dizziness and weight gain were the most frequent observed adverse events with alpha-dihydroergocryptine and flunarizine, respectively. Based on the overall improvement in migraine parameters, alpha-dihydroergocryptine can be recommended for use in migraine prophylaxis.