Objectives: The purpose of this study was to evaluate the clinical outcome and the changes in disc position, mobility, and morphology in patients with temporomandibular joint closed lock in response to arthroscopic lysis and lavage versus arthrocentesis using magnetic resonance imaging (MRI). Materials and methods: 12 Patients with temporomandibular joint closed lock and had remained refractory to nonsurgical treatment for at least 3 weeks without resolution of the problem was included in this study. They were assigned in one of two equal groups: Group 1: Arthroscopic lysis and lavage will be performed. Group 2: Arthrocentesis will be performed. All patients were assessed clinically and radiographically preoperatively, one week and 3 months postoperatively. Results Throughout the study periods, there was a statistically significant increase in mean MIO in both groups and insignificant difference between the two groups regarding the percentages increases in MIO.Throughout the study periods, there was a statistically significant decrease in mean Helkimo index score in both groups. On Comparing between the two groups, Group I showed statistically significantly higher mean percentages decrease in Helkimo index scores than that in Group II. Qualitative analysis of MRI Comparison of characteristics between the arthroscopic and the arthrocentesis joints is Both groups showed improvement in the evaluated parameter by time. Postoperatively, there was no statistically significant difference between the two groups with regard to disc position, disc mobility and disc configuration. However, arthroscopy group showed statistically significant higher prevalence of condylar translation than arthrocentesis grouptatistically significant difference existed at the end of the study Conclusion: The efficacy of TMJ arthrocentesis and arthroscopy for treatment of closed lock is emphasized once again to reduce symptoms of pain and limited mouth opening. However, the clinical efficacy of arthrocentesis is somewhat inferior to that of arthroscopic surgery. Nevertheless, its simplicity makes it the treatment of choice when conservative therapy failed.