OBJECTIVES: The objective of this study was to describe the frequency of TMD diagnoses in a patient population for comparison with the available literature. METHODS: Five hundred twenty consecutive patients seeking TMD treatment underwent a Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) assessment. The prevalence and age distribution of the different RDC/TMD axis I and II diagnoses were described. RESULTS: Muscle disorders, disk displacements, and other joint disorders were diagnosed respectively in 56.4%, 42.0%, and 57.5% of patients. Sixty percent of patients had depression symptoms, 76.6% had somatization, and 21.8% presented high levels of pain-related impairment. Disk displacements were more frequently diagnosed in the younger-aged, other joint disorders in the older-aged, and muscle disorders in the middle-aged subjects (ANOVA for mean age comparison, F = 3.355; P = .002). CONCLUSIONS: These distribution frequencies of TMD diagnoses provide insight into the epidemiology of this disease.