SYNOPSISFifteen families including 35 patients with chronic headache showing electroencephalographic (EEG)abnormalities and dysautonomia are reported on. Nine families including 18 patients with chronicheadache, without EEG abnormalities, served as controls. In the patients with EEG abnormalities, sixpatients (17.1%) suffered from common migraine, 28 (80.0%) from muscle contraction headache and one(2.9%) from combined headache. All the patients had 6‐7Hz EEG abnormalities such as 6‐7Hz slow waves,6‐7HZ spike&wave complexes and 6‐7Hz positive spikes. Most of the patients (77.1%) manifesteddysautonomic symptoms. These symptoms were observed in only 16.7 per cent of the patients with afamily history of headache, without EEG abnormalities. In chronic headache patients, it is suggested thatthere is a group with hereditary dysrhythmic headache characterized by dysau