A prospective study of 100 children aged 2-17 years (68 girls) with juvenile rheumatoid arthritis (JRA) was initiated to follow changes in the temporomandibular joint (TMJ), growth of the craniofacial complex and development of the dental occlusion, and to relate the findings to clinical and laboratory parameters. The mean age at onset was 5.5 years. The debut type was acute febrile in 14, pauciarticular in 64, and polyarticular in 22 patients. At examination, at mean age 9 years, 45 patients had pauci- and 55 polyarticular JRA. Definite radiographic TMJ changes were found in 41 patients (unilaterally in 17). 130 children without joint disease served as controls. Of the patients with radiographic TMJ changes, 65% had clinical symptoms and/or signs, the most frequent being restricted mouth opening. Of the patients without radiographic TMJ changes, 19% had uncertain clinical findings (pain, tenderness or slightly restricted mouth opening). Radiographic TMJ changes were significantly related to early onset of JRA, long disease duration, actual polyarticular type, high disease activity, impaired functional capacity and general health, splenomegaly and kidney involvement, low hemoglobin and high gammaglobulin concentrations. A significant relationship was also found with radiographic changes of the cervical spine. Radiographic examination seemed essential for the diagnosis of TMJ arthritis.