The aim of the present thesis was to investigate different aspects of temporomandibular disorders (TMD) and pain such as prevalence, diagnostics, and treatment among adolescents. The reliability of a questionnaire and the clinical examination and diagnoses according to the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) were assessed. Overall, we found it possible to assess and diagnose TMD in adolescents in a reliable way. The prevalence of TMD pain, gender differences, and the need for treatment were investigated among 864 adolescents from a Public Dental Service clinic. Seven percent of the subjects received a pain diagnosis according to the RDC/TMD, and the prevalence was higher among girls than boys. More subjects with TMD pain reported school absence and analgesic consumption compared to controls. Approximately every second subject who reported TMD pain also perceived a need for treatment. In an evaluation of psychosocial and dental factors, the following were found to play an important role in adolescents with TMD: stress, somatic complaints, and emotional problems. Three treatment methods were compared in a randomized controlled trial: brief information only, brief information and occlusal appliance, and brief information and relaxation therapy. In the brief information and occlusal appliance group, 60%--significantly more than in the other two groups--experienced a reduction of at least 50% in TMD pain. The influence of somatic and emotional stimuli was evaluated, and we found that adolescents with TMD pain were significantly more sensitive to not only aversive somatic but also pleasant somatic stimuli compared with healthy controls. The results suggest that not only nociceptive but also cognitive processes are implicated in chronic pain states in young TMD subjects. In conclusion, TMD pain is more common in girls than in boys and affects daily life. TMD pain in adolescents can best be improved by traditional treatment with occlusal appliance combined with brief information.