The first aim of this thesis was to investigate the prevalence of temporomandibular disorder (TMD) pain in adolescents an a Swedish county and whether there were differences in patient age and gender and in treatment given for TMD pain by dentists in Public Dental Service (PDS) clinics. The epidemiological variable TMD-S was introduced in the PDS in Ostergötland County, Sweden, in 2000 and is recorded for all adolescents aged 12-19 at the annual routine examination. Self-reported TMD pain in this investigation was based upon the response of the subjects to two questions: (1) Do you have pain in your temples, face, temporomandibular joint, or jaws once a week or more? and (2) Do you have pain when you open your mouth wide or chew, once a week or more? Dental records of 200 patients with TMD pain were randomly selected from the population to evaluate treatment given for TMD. Among 28,899 participating adolescents, 4.2% reported TMD pain. Prevalence increased with age, a significant difference was seen between boys and girls, and 34% of patients with TMD pain received TMD-relared treatment in dental clinics. The second aim was to evaluate the reliability and validity of self-reported TMD pain in 120 adolescents, 60 with self-reported TMD pain and 60 age- and sex-matched controls without TMD pain. All adolescents were examined twice at a PDS clinic. At the first examination, self-reported TMD pain was recorded for each patient. At the second examination, a clinical examination was made blind to the patients' self-report of pain symptoms, after which self-reported TMD pain was again recorded. The clinical examination was based upon the Research Diagnostic Criteria for TMD (RDC/TMD). Test-retest reliability of 0.83 (kappa) was found for the two questions. Sensitivity was 0.98 and specificity 0.90 for assessments made on the same day and 0.96 and 0.83, respectively, for assessments made 2-4 weeks apart. The third aim was to evaluate incidence, by age and gender, and temporal patterns of TMD pain in adolescents. This 3-year longitudinal study was carried out at all PDS clinics from 2000 to 2003. All individuals aged 12-19 years in the county who visited the clinics for annual examinations were eligible for the study. Overall, the annual incidence of TMD pain among 2255 participating adolescents was 2.9%. Incidence among girls (4.5% was significantly higher than in boys (1.3%). Incidence increased with age in girls and boys, although less so in boys. These adolescents were re-examined annually for 3 years, and a fluctuating pattern of TMD pain was common. The fourth and final aim was to investigate gender and age differences in pain behavior, jaw function, and psychosocial status in adolescents with self-reported TMD pain. A postal questionnaire was sent to 350 consecutive patients with self-reported TMD pain and 350 healthy age- and sex-matched individuals aged 12-19 years 2-4 weeks after their annual dental examination. The groups were divided into younger (age 12-15) and older (age 16-19) groups. The TMD and control groups differed significantly in most variables related to pain characteristics and psychosocial and behavioral factors. Multiple pain sites were significantly more common in the TMD than in the control group, but there were no gender differences. For adolescents reporting pain once a week or more, no gender differences were seen in pain intensities. Jaw function limitation, depression scores, and perceived need for TMD treatment were significantly higher overall in girls than in boys. Almost one-third of older girls, compared to one out of ten older boys, reported school absences and analgesic consumption because of their TMD pain. Older girls had significantly higher Graded Chronic Pain Scale scores than older boys. In conclusion, TMD pain increases with increasing age in adolescents and is more common in girls than in boys. A fluctuating pain pattern can be seen. TMD-S, with two self-report questions, has very good reliability and validity, and can be recommended for screening adolescents for TMD pain. TMD pain seems to have a greater Impact on girls than boys. particularly in ages 16-19 years.