Disc displacement, deformation, perforation or osteoarthritis may induce the joint space narrowing. This study was designed to get the normal joint space width which could be used as a standard comparing with damaged joints. Twenty asymptomatic volunteers' MR images were evaluated and coronal images of thirty joints having normal disc position in sagittal and coronal views, were selected. The joint spaces were measured at center, medial and lateral side on the coronal views. In normal joints, the mean joint space was 3.57+/-0.63mm at center, 2.77+/-0.51mm at medial and 2.41+/-0.41mm at lateral side of mandibular condyle. The mean of joint space of male was wider than that of female at center, but not significantly different at medial and lateral side of the condyle.