Background: The objective of this study was to investigate the difference of the temporomandibular joint (TMJ) size between deviated and nondeviated sides of the mandible in adult patients with mandibular deviation. Material and Methoeds:TMJ size, of 28 patients was examined clinically and by magnetic resonance imaging (MRI). Twelve age- and sex-matched control subjects were also used to evaluate which side of the mandible in patients was similar to the control. Results: The TMJ on the deviated side showed a smaller condyle than the non deviated side and those in the controls. Conclusions: Our results suggest that the deviated side was the abnormal side and may have some association with mandibular deviation. Keywords: Mandibular deviation, Magnetic resonance imaging (MRI), Temporomandibular disorders (TMD)