Objective Temporomandibular disorders (TMD) have often been related to sleep bruxism and elevated nocturnal masseter muscle activity (NMMA). However, previous studies have revealed controversial results, and the role of somatization, depression and anxiety has not been studied in this context. The aim of this study was to investigate the association between NMMA and pain intensity, TMD related symptoms, somatoform symptoms, depression, and anxiety in chronic TMD. Methods Thirty-six subjects with chronic painful TMD, 34 subjects with pain free bruxism, and 36 healthy controls recorded their nocturnal masseter muscle activity during three consecutive nights with portable devices. In addition, participants completed pain diaries and questionnaires. Diagnoses were established using the research diagnostic criteria for TMD. Results Subjects with chronic TMD reported a reduced general health state (p <.001), higher levels of somatoform symptoms (p <.001), depression (p <.05), and anxiety (p <.001) compared to control subjects with or without sleep bruxism. The amount of NMMA did not differ significantly between the groups. In subjects with TMD, pain intensity was not related to NMMA. However, higher NMMA was related to higher intensity of jaw related symptoms such as headache or tinnitus, and higher somatization in general. Conclusion Chronic TMD is associated with elevated levels of psychopathology. These findings suggest a common link between NMMA, somatization, and symptom intensity in chronic TMD.