One hundred ACL insufficient knees were followed for an average of 3.5 years after arthroscopic partial meniscectomy had been performed. Fifty-two percent of the patients obtained a satisfactory result and 41% were able to participate in strenuous sports activities. The arthroscopic partial meniscectomy reduced pain and swelling in a high proportion of cases, but stability was only marginally improved. Negative prognostic factors were: sex (female), generalized laxity, contralateral recurvatum of more than 10 degrees, complete as opposed to partial ACL lesions, Grade III tibiofemoral or patellar chondromalacia, associated peripheral ligamentous laxity, pivot shift of Grade II or greater, and anterior tibial displacement of more than 5 mm as measured with the KT-1000 knee arthrometer.