Temporomandibular joint (TMJ) disorders have been collectively grouped as myofascial pain-dysfunction syndrome (MPDS) or temporomandibular joint dysfunction syndrome (TMJDS). In the past, these terms have been used synonomously to describe a set of clinical signs and symptoms that include pain in the TMJ and muscles of mastication, limited or deviant opening of the mandible, and/or joint sounds. The present study segregated two major subgroups subsumed within this diagnostic classification and assigned them to a myogenic facial pain (MFP) group and a TMJ internal derangement (TMJID) group. Previous studies may have included both of these disorders as MPDS/TMJDS. While some signs and symptoms are similar, the primary differentiation is based on meniscus displacement present with TMJID patients and pain distribution patterns between the two groups. While MFP/TMJID patients comprise the majority of the facial pain population, a third major group of patients is encountered, being classified under the diagnostic appellation of atypical facial pain (AFP). Patients with AFP usually complain of vague and wandering pain in the maxilla or mandible; however, no identifiable source of infection or organic disease can be uncovered. One hundred fifty patients seeking consultation and care for facial pain met the criteria for inclusion into one of three clinical groups. The groups were compared for age, sex, duration of symptoms, bruxism and/or clenching habits, and disturbed sleep patterns. Differences in surface electromyographic levels from the facial and cervical muscles were also examined. Minnesota Multiphasic Personality Inventory (MMPI) scores from 95 subjects were compared with self-report measures of depression and anxiety. It was concluded that subcategorization of myofascial pain dysfunction patients into a MFP and TMJID group is justified on the basis of psychometric differences, clenching habits, masseter EMG levels, and male:female raio. Furthermore, psychopathological factors are more significant among MFP and AFP subjects than TMJID patients