Clinical features of 750 patients seen with an acute migraine attack at the Copenhagen Acute Headache Clinic were analyzed. In 47% pain quality was pulsating, in 42% pressing and in 11% other types. Unilateral pain was seen in 56% and bilateral in 44%. Half the patients had interictal headaches. In patients with severe pain the quality was significantly more often pulsating. Patients with bioccipital headache had significantly less visual disturbances than patients with other pain locations. On the basis of these findings the currently accepted definitions of migraine are criticized and a new and more precise definition is proposed. Considerable amounts of tenderness was found in the chewing and neck muscles. The location of tenderness corresponded largely to the location of the pain. Patients with associated symptoms and with pulsating pain quality had significantly more tenderness. There was no correlation between the duration of the attacks and the amount of muscle tenderness. Based on these data and other clinical evidence it is proposed that the muscle tenderness during a migraine attack is not secondary to migrainous pain but rather yet another manifestation of the attack and probably responsible for the pain.