This is the first population-based epidemiologic study of chronic headache in South Korea. The diagnosis and classification of headache was according to the criteria of the International Headache Society. Sixty-eight percent of the studied population experienced headache during the preceding year. The estimated prevalences were 22.3% for migraine (male 20.2%, female 24.3%) and 16.2% for tension-type headache (male 17.8%, female 14.7%). In migraine, the 15-to 19-year age group showed maximal prevalence in both sexes (male 28.5%, female 34.7%). The prevalence of tension-type headache was highest in the 50- to 59-year age group in men(24.2%) and in the 20- to 29-year age group in women(20.2%). In migraine, headache intensity was more severe in women than in men, but in tension-type headache there was no difference in the severity of headache between the sexes. Phonophobia was the most common associated symptom of migraine (65.1%). In the migraine with aura group, the most common aura was visual disturbance, including scintillation and image distortion (82.3%). Only 24.4% of migraineurs and 12.3% of patients with tension-type headache had ever consulted a doctor for headache. The prevalence of migraine was not lower than in western countries and much higher than in previous studies conducted in other Asian countries.