The authors report 4 cases of rapid lateral femoro-tibial chondrolysis following arthroscopic lateral meniscectomy. All patients were young athletes. At the time of meniscectomy, the cartilage of the lateral compartment was normal. Only one meniscectomy was done with the Ho Yag laser. Clinical symptoms were always identical: pain and important swelling, persisting despite intra articular injections of corticosteroids. A second-look arthroscopy was performed after a mean delay of 6 months (5 to 8), showing numerous cartilaginous debris floating in the joint (like in a chondromatosis disease) and a severe cartilaginous damage in the lateral compartment (grade 3 or 4). Swelling disappeared after arthroscopic lavage followed in two cases by a non weight bearing period of one to two months. But X-rays always demonstrated a narrowing of the lateral joint line on flexion-full weight bearing AP views. Rapid chondrolysis is a rare and severe complication of lateral meniscectomy. The etiology, which is mechanical, is not known. It probably represents an acute form of chronic, slow chondrolysis which is frequent after lateral meniscectomy. Rapid chondrolysis should be treated urgently by the following protocol: arthroscopic lavage, intra articular injections of corticosteroids and non weight bearing period.