76 cases of cluster headache are reviewed. Besides confirming established notions, the present study calls attention to the following points: (a) the peculiar behaviour of patients during the attacks does not appear explainable in simple terms of reaction to pain; (b) the occurrence of ECG abnormalities during the attacks in addition to bradycardia; (c) the well-known tendency of cluster headache attacks to recur at the same time of day, has in our cases a very high peak at 3 p.m., and (d) when the attacks occur in sleep hours, the time relationship with REM sleep stage is confirmed in our cases which have been recorded at night.