Introduction: Internal derangement (ID) of TMJ is the most common type of temporomandibular disorders after muscle disorders and includes all disorders related to incoordination and dislocation of disc and condyle. Anterior disc displacement without reduction or closed lock will happen if the disc or condyle displaces severely or if the disc traps in the space in front of the condyle accompanied with reduction in maximum mouth Opening. The purpose of this study was to evaluate reliability of clinical diagnosis of disc displacement without reduction (closed lock) by using magnetic resonance imaging as the Gold standard. Method: This cross-sectional study was carried out on 10 patients who had referred to Dental school of Mashhad University with the symptoms of ID and were assigned a clinical diagnosis of disc displacement without reduction. Sagital and coronal MR images were obtained with 0.5 Tesla magnetic resonance system, with the jaw in closed and maximum opening position subsequently to establish the corresponding diagnosis of disc-condyle relationship. The data analysis included kappa statistic and calculation of positive predictive values and sensitivity Results: The overall diagnostic agreement for disc displacement without reduction was 0.22 with a corresponding kappa value The predictive value for clinical diagnosis of disc displacement without reduction was 20% and the sensitivity was 100% Conclusion: According to the results, clinical diagnostic criteria for disc displacement without reduction is not reliable and patients assigned clinical TMJ-related diagnosis of disc displacement without redaction may need to be supplemented by evidence from MRI to determine the functional disc – condyle relationship.