The cases of a woman and her son with a long history (24 and 9 years, respectively) of hemiplegic migraine are presented. The mother demonstrated exclusively right-sided paralysis; in the son, paralysis occurred on each side. Electroencephalograms recorded during the attacks were characterized by pseudoperiodic slow sharp waves over the hemisphere contralateral to the hemiplegia. Between attacks the neurological examination and EEG were normal. CT scans performed during and between attacks showed no abnormalities.