Patients with migraine are known to be at risk for stroke. It has been reported that in a group of patients with cerebral ischemia and the Leiden mutation of factor V, 67% had classical migraine. We have studied the frequency of this mutation in a group of Italian children and adolescents affected by migraine with aura. The Leiden mutation was detected in 2 (3.5%) of 57 patients and in 8 (3.7%) of 219 controls. The 2 patients carrying the mutation had no peculiar characteristics as compared with the rest of the migrainous population. In our study, the frequency of the Leiden mutation in patients was not different from that of controls. These data contrast with those collected in the Finnish population and in a group of northwestern Italian adult patients, but agree with results previously reported from The Netherlands.