A multicenter study is presented on 80 patients who underwent ACL reconstruction using a Dacron (E.I. Du Pont de Nemours and Co., Wilmington, DE) ligament prosthesis. Patient selection was based on a history of a failed autologous reconstruction and/or primary repair of the ACL. These selection criteria are unique and have not been previously reported in the literature. The frequency of prior intraarticular ACL surgery was 1.24 procedures per patient and 1.68 when combined with prior extraarticular reconstructions. Forty-one patients had a mean followup of 28 months (24 to 42 months). The mean followup for all of the patients was 21 months. The graft was augmented with autologous tissue in 59 cases and used as a pure prosthesis in the rest. Functionally, the mean Lysholm score improved from 40 to 81 points. The percentage of a combined excellent/good Lysholm rating increased from 6% to 60%. The Tegner activity rating level improved from 2 to 4. The percentage of a negative Lachman sign, anterior drawer, and pivot shift was approximately 75% at followup. There was no significant difference between the results of augmentation and nonaugmentation cases, indicating that the graft acts as a permanent prosthesis rather than as a scaffold or stint. The patients showed a significant improvement considering their preoperative global instability.