The incidence of migraine in a general population has been assessed in few longitudinal studies, and the incidence of tension-type headache has never been assessed. The authors aimed to assess the incidence of migraine and tension-type headache in Denmark by conducting a 12-year follow-up study of a general population (1989-2001). The design and methods of follow-up replicated the baseline study exactly, including use of the International Headache Society's diagnostic criteria and administration of headache diagnostic interviews by a physician. Of 740 persons aged 25-64 years examined in 1989, 673 were eligible in 2001 and 549 (81.6%) participated. The incidence of migraine was 8.1 per 1,000 person-years (male:female ratio, 1:6), and the incidence of frequent tension-type headache was 14.2 per 1,000 person-years (male:female ratio, 1:3). Both rates decreased with age. The incidence of migraine was higher than that previously calculated from cross-sectional studies. Risk factors for migraine were familial disposition, no vocational education, a high work load, and frequent tension-type headache. For tension-type headache, risk factors were poor self-rated health, inability to relax after work, and sleeping few hours per night. The gender difference for tension-type headache differed from that for migraine, and no association with educational level was observed.