An epidemiologic study of clinical signs and symptoms of temporomandibular disorders (TMD) was conducted with a probability sample of adults enrolled in a major health maintenance organization (HMO). This report presents data from a first wave field examination and interview conducted by trained, calibrated dental hygienist field examiners. Significant gender differences for vertical jaw opening measures were observed but no significant age differences were found for the distribution of clinically relevant findings. Clinic cases showed smaller amounts of vertical range of jaw motion but did not differ from community cases or controls on extent of lateral, protrusive, or retrusive mandibular movements; on classification of occlusion; or on dentally related variables. Clinic cases had more pain during all jaw excursions as well as during muscle and joint palpation. Joint clicking sounds were also observed more frequently in clinic cases.