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BACKGROUND: Temporomandibular disorder (TMD) is a collective term that encompasses many clinical problems involving the masticatory muscles, temporomandibular joints (TMJ) and associated structures and it has high prevalence among populations. OBJECTIVES: Because Brazilian studies have used the instrument proposed by Da Fonseca et al. (1994) to diagnose the severity of TMD, this study was conducted to investigate and estimate the internal consistency and reproducibility of this method. METHODS: We used a probability sampling design to select 1230 participants over the age of 18 years who were living in the city of Ribeirão Preto, SP, Brazil. The interviews were conducted by a single interviewer over the phone. The internal consistency was analyzed by calculating the Kuder-Richardson coefficient (kr-20), and kappa statistics (K) were used to estimate the reproducibility. RESULTS: The internal consistency of the questionnaire was 0.5594, thus indicating that validation was lower than desired. Questions 1, 2, 3, 6 and 7 had greater contribution towards the total kr-20 coefficient, and the consistency of the instrument was higher when it was composed only of these questions (0.7044). 'Good' and 'Excellent' reproducibility was observed for these same questions. CONCLUSIONS: Based on these data, it is suggested that the questionnaire proposed by Da Fonseca et al. (1994) should be adapted to include only questions 1, 2, 3, 6 and 7 of the initial version. This would help improve the reliability of the instrument. The need for validation studies must also be emphasized to ensure that the new version of the instrument has adequate psychometric characteristics. [ABSTRACT FROM AUTHOR]