The purpose of the current study was to evaluate the pattern of age distribution of temporomandibular disorders (TMD) and to identify prevalence peaks for the different diagnoses. The study sample (N = 383; F:M ratio = 3.9; mean age range 41.7 +/- 17 years) consisted of patients seeking treatment for TMD and who were assessed in accordance with the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) version 1.0 guidelines. The sample was divided into four age groups on the basis of percentile-derived intervals to compare prevalence of different diagnoses in relation to age. The pattern of clinical diagnoses changed with increasing age. The peculiar distribution of RDC/TMD axis I diagnoses, with relation to age, mainly affected the disorders trend of groups II and III, with the former decreasing with age from about 62% to 40% and the latter increasing from 75% to almost 95%. Two distinct age peaks were identified for the prevalence of the main clinical marker of group III diagnosis of arthrosis/arthritis, viz., joint crepitus sounds (N = 104, mean age range 51.9 +/- 14.5), and for the prevalence of all other diagnoses in patients without joint crepitus (N = 279, mean age range 37.9 +/- 16.4). The hypothesis that TMD patient populations may be composed of at least two diagnostic subgroups in relation to age, and that the presence of clinically diagnosed degenerative joint disorders may be a key discriminating factor, was supported. The external validity of the results from this investigation needs to be confirmed by multicenter and cross-cultural studies.