Purpose: Urgent diagnosis and treatment of the septic arthritis is required. The purpose of this study is to review to correlate preoperative MRI findings with arthroscopic findings in septic arthritis of the glenohumeral joint. Materials and Methods: Eleven patients with acute septic arthritis of the glenohumeral joint were treated with combination of arthroscopic lavage, debridement, and systemic antibiotics. The arthroscopic staging of infection was made based on the modified criteria of $G"{a}chter$ and five major findings of MRI were marked in each stage of septic shoulder. Results: Bone and cartilage erosion was the end stage finding and two patients with all five positive findings had failed with arthroscopic treatment. Reactive bone marrow edema was evident in the greater tuberosity. Joint effusion, synovial thickening and soft tissue edema were rather non-specific finding and presented in all stages of septic shoulder. Conclusion: Diffuse marrow edema with metaphyseal cyst formation in the preoperative MRI implied advanced stage of septic arthritis, which may fail with arthroscopic debridement.