Patients diagnosed as suffering from common migraine according to the "Ad hoc committee" criteria of 1962 have been studied as for type of unilaterality of headache. Patients, with trauma to the face, head, and neck were excluded, together with patients with the faintest suspicion of aura and those with chronification of the headache. Common migraine criteria, as stipulated by the IHS and Vahlquist, were counted in every patient (n = 32), except the laterality which was a free variable (a total of 8 variables remaining). For comparison, as far as the number of migraine criteria is concerned, a group of cervicogenic headache patients was also studied (n = 30). Unilaterality with side shift of pain was present in 75% in the common migraine group; in 34% of the patients, a combined pattern, i.e. bilateral headache + unilaterality with sideshift was present. Common migraine, therefore, just as classic migraine, seems to be a headache characterized by unilaterality with side alternation of pain. Common migraine criteria were present to a high degree in common migraine patients selected in this way, i.e. ca. 6.8 of a maximum of 7. In cervicogenic headache, the corresponding figure was ca. 3.8 (of a maximum of 7). These figures are statistically significantly different (p < 1.3 10(-11), Mann-Whitney test). Still, the level of criteria is relatively high in cervicogenic headache, and 6 of 30 patients would fulfil the IHS common migraine criteria.