The aim of this study was to determine the prevalence of self-reported chronic idiopathic pain among adolescents in relation to age and gender, and to explore how pain interferes with daily activities. The study was performed in Nord-Trøndelag County, Norway in 2006-2008. All adolescents were invited to participate; the response rate was 78%. Participants completed a comprehensive questionnaire, including questions about pain and interference with everyday life. Chronic idiopathic pain was defined as pain at least once a week during the last 3 months, not related to any known disease or injury. The final study population, with complete pain questionnaires, consisted of 7373 adolescents aged 13-18 years. Chronic pain was reported by 44.4% of the participants, and 25.5% reported pain in at least 2 locations. Chronic idiopathic musculoskeletal pain was most prevalent (33.4%), and the neck/shoulder was most commonly affected. Musculoskeletal pain in 3 or more locations was reported by 8.5%. Pain almost daily was reported by 10.2%. More girls than boys reported pain. In girls, the prevalence of pain increased with age. A high number of pain-associated disabilities were reported, and 58.5% described difficulties doing daily activities in leisure time. Subjective disabilities were higher in girls, and increased with the frequency of pain and the number of pain locations, as shown by high disability in adolescents with musculoskeletal pain in 3 or more locations. Chronic idiopathic pain, especially multisite pain, is common among adolescents, and those suffering from it report a major impact on several areas of daily living.