BACKGROUND: To investigate the difference in diagnostic reliability between self-instructed examiners and examiners taught in a Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) course and if the reliability of self-instructed examiners improves after the course. METHODS: Six examiners were divided into three groups: (1) formal two-day training and calibration course at a DC/TMD training center (Course group), (2) self-teaching through documents and movie (Self group) with three examiners on each and the Self group later participated in the course (Self + course group). Each group examined sixteen subjects, total of 48 volunteers (36 patients with TMD and 12 asymptomatic) and the reliabilities in relation to the diagnoses derived by a Reference Standard Examiner were compared by Cohen's Kappa coefficient. RESULTS: The reliability was good to excellent in all three groups of examiners for all DC/TMD diagnoses, except for Myofascial pain with referral in the Self + course group. The course seemed to improve the reliability regarding Myalgia and Arthralgia at the same time as the examiners experienced the course to be valuable for self-perceived ability and confidence. CONCLUSIONS: This study shows that the diagnostic reliability of formal DC/TMD training and calibration and DC/TMD self-instruction are similar, except for subgroups of Myalgia. Thus, self-instruction seems to be possible to use to diagnose the most common TMDs in general dental practice. The course further improves the reliability regarding Myalgia and Arthralgia at the same time as the examiners experienced the course to be valuable for self-perceived ability and confidence.