A retrospective study was performed to determine the etiology of failed primary anterior cruciate ligament (ACL) reconstruction and evaluate the clinical results of revision ACL surgery. From January 1989 to January 1996, 90 patients with failed ACL reconstructions underwent revision ACL surgery. The etiology of failed ACL reconstruction included 47 surgical technical errors, 22 traumatic reinjuries, 7 lack of graft incorporation, 3 loss of motion, 3 related to synthetic grafts, and 8 alignment or combined ligamentous instability patterns not addressed. Of 52 revision ACL patients with minimum 2-year follow-up, 43responded to a questionnaire and underwent a comprehensive physical examination. The Hospital for Special Surgery knee ligament evaluation revealed 63% good/excellent results. Objective laxity test revealed 77% of all patients had 0/ϩ ϩ1 grade on Lachman and a mean 2.86-mm KT 1000. The overall results of revision ACL surgery are encouraging in providing symptomatic relief and restoring stability; however, they are significantly lower than primary ACL surgery.