Purpose: The purpose of this study was to evaluate prognostic factors of ankle arthroscopy and the effectiveness of high anteromedial and anterolateral portals in diagnosis and treatment for various disease entities. Materials and Methods: The results of ankle arthroscopy were evaluated between March 1992 and January 2000 by one surgeon. Total 169 patients who were followed for a minimum of 12 months, were included in this study. Using high anteromedial and high anterolateral portals, all procedures were done with accessory portals if necessary. A functional evaluation was performed using the Karlsson score and questionnaire subjectively. Results: Fifty-six synovial impingement, 48 osteochondral lesion on talus, 10 impingement exostosis, 8 loose body, 27 osteoarthritis and chondromalacia, 10 postfracture fibrosis, 3 lateral plica, and 1 pigmented villonodular synivitis(PVNS) among 169 patients were diagnosed. Patients with the former four groups had satisfactory results and the latter four groups had not. Remaining 6 patients underwent arthroscopic arthrodesis, and 5 had satisfactory results. Conclusion: Using high anteromedial and anterolateral portals, we could get better visualization of talar dome and posterior chamber of ankle. For better clinical results, in ankle arthroscopy, not only operative skill but also proper indications are important. In case of synovial impingement after trauma, arthroscopy should be considered within one year after initial trauma. There were little correlation between the radiographic findings and arthroscopic findings of articular cartilage in osteochondral lesion of talus, and it is better to determine treatment modality based on the arthroscopic or MRI findings. Osteochondral lesions were treated successfully only when they were traumatically induced and localized without diffuse chondromalacia of talus and tibia.