The familial occurrence and mode of inheritance were analysed in families with migraine without aura (MO) and migraine with aura (MA). The probands were found among 4000 persons from the general population. All persons with MA were included as probands, and an equivalent number of probands with MO was selected as a random sample among those with MO. Spouses and first-degree relatives were blindly interviewed. All interviews were performed by one neurological research fellow. The distinct familial patterns indicate that MO and MA have a different aetiology. Compared with the general population, the first-degree relatives of probands with MO had a 1.9-fold increased risk of MO while spouses had a 1.5-fold increased risk of MO, indicating that both genetic and environmental factors are important in MO. The first-degree relatives of probands with MA had a four-fold increased risk of MA while spouses had no increased risk of MA, indicating that MA is determined largely by genetic factors. The complex segregation analysis indicated that both MO and MA have multifactorial inheritance without generational difference.