The role played by synovial plica in internal derangement of the knee has been increased recently. A clinical application of arthroscopy of the one hundred eighty patients were performed, and eighteen patients with a symptomatic plica were successfully managed and followed by arthroscopic surgery at the department of orthopaedic surgery, Soon Chun Hyang University Hospital from May 1983 to May 1984. The results were summerized as follows; 1. Arthroscopy is the most accurate diagnostic and operative methods for the investigation of the incidence, pathology, clinical significance and treatment of the synovial plica. 2. The incidence of the mediopatellar plica in our view was 41% that is, 74 of 180 symptomatic knee. 3. Arthroscopy is a practical and valuable procedure with minimal associated morbidity or complication. 4. The increased accuracy of diagnosis help to avoid unnecessary operations and to be basic methods of treatment on a better knowledge of the pathology.