Aim: To estimate the incidence of temporomandibular disorder (TMD) pain among Swedish adolescents by age and gender and to describe the temporal patterns of TMD pain. Methods: This 3-year longitudinal study was carried out at all Public Dental Service clinics in a Swedish county from 2000 to 2003. All individuals aged 12 to 19 years in the county who visited the clinics for annual examinations were eligible for the study. Results: Overall, the incidence of TMD pain among all adolescents was 2.9% annually among 2,255 participating adolescents. Incidence among girls was significantly higher than in boys, 4.5% versus 1.3%, respectively. Incidence increased with age in girls and boys, although less so in boys (3.0% to 6.9% versus 1.7% to 2.6%). These adolescents were re-examined annually for 3 years, and a fluctuating pattern of TMD pain was common. Overall, 11.4% of all subjects reported TMD pain on at least 1 occasion; 88.6% of the cohort remained pain-free. Of those reporting TMD pain, 4.7% could be defined as intermittent cases, 3.1% were single-incident cases, 0.9% were recurrent cases, and 0.9% had continuing pain for 1 or 2 years. Conclusion: The incidence of self-reported TMD pain among Swedish adolescents aged 12 to 19 years increased with age, particularly among girls. The pattern of pain in most adolescents fluctuated over time. Less than 1% of the cohort had continued pain over each year, and the majority of these subjects were girls. Keywords: cohort studies, epidemiology, pain, sex factors, temporomandibular joint disorders