Four of five members of a family complained of repeated attacks of hemiplegic migraine, migraine with aura of different types, or migraine without aura. The hemiplegia always outlasted the headache and was often accompanied by altered consciousness, aphasia, and, in one patient, coma; in this latter patient, the ictal EEG, recorded during two attacks, showed delta activity in the hemisphere contralateral to the hemiplegia. At least 2 months after their latest attacks, three patients showed dyscalculia, attentional disturbances, and impaired long-term verbal memory on neuropsychologic assessment. There were no cognitive disturbances in the unaffected relative. The severity of cognitive impairment appears to be correlated with migraine history. We attempt to classify these cases according to the criteria of the International Headache Society.