EEGs of 55 subjects with classic or common migraine were correlated with headache subtype, age of onset, duration of illness, family history, and time span either from last headache or medication. Eleven patients (20%) had abnormal EEGs: five were diffusely slow, one demonstrated bitemporal slowing, one generalized spikes, and two each showed either a photoconvulsive response or excessive buildup to hyperventilation. EEG abnormalities did not correlate chronologically with medication or headache. Six of 30 patients with headache andor medication within 48 hours of the EEG had abnormal records, a number not statistically different from the five of 25 who had abnormal EEGs in the absence of headache or medication in the previous 48 hours. EEG abnormalities in migraine, while varied and nonspecific, do persist during asymptomatic intervals. This suggests more permanent alterations of cerebral physiology than can be accounted for by transient vascular changes during migraine attacks themselves.