Objective To evaluate the influence of total removal of lateral discoid meniscus in lateral displacement of the patella, investigate its mechanism and clinical management. Methods From January2004 to March 2009，a series of 96 patients was involved in this study, included 44 men and 52 women with a mean age of 25 years (range 14-38 years) and including 50 left knees and 46 right knees. Total meniscectomy were performed in 96 knees (96 patients) to treat a discoid lateral meniscus. Radiographs and computerized tomography were made for every patient to evaluate the change of joint space width of the tibiofemoral, tibiofemoral angle, lateral displacement of the patella and distance between the tibial tuberosity and the trochlear groove (TTTG) after meniscectomy. The statistical evaluation was carried out by the paired two-tailed t-test. Results All patients were followed up12.5years. The tibiofemoral angle, space width of the tibiofemoral , lateral displacement of the patella and distance between the tibial tuberosity and the trochlear groove (TTTG) were 7°±1.5°、5.8±1.0mm、0、11±2 mm before surgery; After the Total meniscectomy, the tibiofemoral angle, space width of the tibiofemoral , lateral displacement of the patella and distance between the tibial tuberosity and the trochlear groove(TTTG)were 15°±2°、3.2±0.5mm、3.2±0.6 mm、23 ±2 mm. There were statistically significant differences between preoperation and postoperation(P<0.05). Conclusion Total removal of complete lateral discoid meniscus can influence lateral displacement of the patella, and occurs patellofemoral arthritis.