A single-center prospective study is presented on 35 patients who underwent anterior cruciate ligament reconstruction using a Dacron ligament prosthesis. All of the reconstructions were performed by the same surgeon, using the same technique. All of the patients had a history of symptomatic chronic ACL insufficiency. The mean follow-up interval for all patients was 50 months. There was an overall failure rate of 37.1% (13 patients), based on the presence of at least one of the following criteria: the presence of a pivot shift; a 2+ or greater anterior drawer or Lachman; instrumented laxity of greater than 3 mm side-to-side translation in 20 degrees of flexion at 89 N; or by arthroscopic documentation. Six of these 13 patients were documented by arthroscopy and 7 were clinical failures. There were 26 patients with only anterior cruciate ligament laxity, and 9 patients with multiple instabilities or failed previous ACL reconstruction ("salvage"). In the group with isolated anterior cruciate ligament insufficiency, the failure rate was 23% (6 patients). In the salvage group, the failure rate was 78% (7 patients). There was a significant improvement in patient performance with respect to clinical laxity, Lysholm scores, and Tegner activity levels at 2 years postoperatively. There has been a subsequent deterioration in the performance of these patients through time.