The prevalence of migraine and cluster headache was investigated in a well-defined homogeneous non-hospital population of 9,803 18-year-old men from east central Sweden. The occurrence of headache was recorded by means of a questionnaire technique which proved to have a high degree of reliability as shown in personal interviews with a randomly chosen series of more than one-fifth of the subjects. Personal interviews were held in all subjects. Personal interviews were held in all suspected cases of cluster headache. Recurrent headache occurred in 4.4% of the cases: migraine in 1.7%; cluster headache in 0.09%; other, non-migrainous headache (MNH) in 2.6%. The majority of subjects had relatively frequent headaches, but only 43% of the migraine and 32% of the MNH subjects had sought medical advice for their complaint. Daily or almost daily consumption of analgetics was reported by 14% of the migraine and 11% of the NMH subjects. Ergotamine tartrate had been used by 15% of those suffering from migraine.Only 4 of the 9 subjects with cluster headache had been to a doctor on account of their headache, and only in one of them had a correct diagnosis been made. One subject had primary chronic symptoms, the remainder suffered periodically from cluster headache. Three subjects had symptoms since the age of 8-9 years.