Anamnestic data and clinical features were accurately investigated in 180 patients with cluster headache; 161 were episodic sufferers and 19 were chronic. A significantly high familial incidence of coronary heart disease was found. The patients' medical history revealed a significantly high incidence of peptic ulcer disease and head injury with brain concussion. It is stressed that the side on which head injury took place is very frequently the same side on which cluster headache is located, although the latency between the two events appears to be a long one. The study of timing of cluster periods suggests, for some patients, a constant, typical temporal pattern not necessarily related to seasons or the months of of the year. Cluster attacks frequently occur during certain periods of the day (onset being most frequent between 1 and 3 p.m.). Cluster headache cannot be considered as a nocturnal headache.