The aim of this study was to examine the prevalence of headache and primary headache disorders like migraine and tension-type headaches among adolescents, and to explore the differences in headache prevalence and frequency by gender and age. This cross-sectional study was conducted in Nord-Trøndelag county, Norway, during the years 1995-97. In total, 8984 (88%) out of 10 202 invited adolescents aged 12-19 years participated in the youth part of the Nord-Trøndelag Health Study [Helseundersøkelsen i Nord-Trøndelag (HUNT)]. The total study population in this study consisted of 8255 individuals after exclusion of invalid questionnaires and students outside the target range of 13-18 years of age. The students completed a comprehensive questionnaire, and one of the questions was whether the students had experienced any headaches during the last 12 months. In addition, 5847 of these students were also subject to an interview in which they were asked whether they had experienced recurring headaches during the last year and, if so, were they classified as migraine (MI), tension-type headache (TTH) or non-classifiable headache. In the total questionnaire-based population, 76.8% reported having had headaches during the last 12 months (69.4% boys and 84.2% girls). Among those who also were interviewed, 29.1% reported having recurrent headaches (21.0% boys and 36.5% girls). The overall 1-year prevalence of migraine was 7%, of tension-type headache 18%, and of non-classifiable headache 4.8%. Higher prevalence rates were found for girls in all age groups and for all headache categories. The overall frequency of recurrent headaches did not vary significantly with age, but girls had significantly more frequent headaches than boys. We concluded that headache in general, and recurrent primary headache disorders like migraine and tension-type headaches, are common somatic complaints among Norwegian adolescents, especially among girls.