We analyzed 31 families selected for an apparently autosomal-dominant mode of inheritance of migraine with aura (MA) in the nuclear family. The nuclear families were expanded with first- and second-degree relatives. All interviews were made by physicians experienced in headache diagnoses. The criteria of the International Headache Society were used. The population relative risk among children in nuclear families was similar to the estimated population relative risk of MA assuming an autosomal-dominant mode of inheritance. The population relative risk tended to decrease among first-degree relatives outside nuclear families and further among second-degree relatives. Both first- and second-degree relatives outside the nuclear families had a statistically significant lower risk of MA than expected. Thus, autosomal-dominant inheritance with or without reduced penetrance was unlikely. Autosomal-recessive inheritance was unlikely because of the unequal sex distribution. Other modes of inheritance were considered as well. Mitochondrial and X-linked inheritance were excluded because of paternal transmission. The female preponderance was too low to explain sex-influenced inheritance. We conclude that MA most likely has a multifactorial inheritance even in high-risk families with MA.