Following initial enthusiasm in the late 1980s, the use of artificial ligament substitutes for anterior cruciate ligament (ACL) reconstruction has declined. However, the disadvantages of donor site morbidity for autologous graft and concerns about cross-infection from allogenic material have resulted in a maintained interest in prosthetic ligament substitutes. This study presents the outcome of ACL substitution using the Leeds-Keio (LK) polyester ligament at a mean of 13.3 years (range 10-16 years). Outcome was assessed using the International Knee Documentation Committee score, the Lysholm knee score, Tegner activity scale and American Knee Society Score and laxity by clinical examination and the Stryker Knee Laxity Tester. Standardized radiographs were taken to assess for evidence of degenerative change. The objective scoring tests showed that all patients experienced some degree of symptoms from their knee but functional impairment varied widely. Of the group, 28% were known to have ruptured their LK ligament and 56% had increased laxity compared with their opposite knee but no correlation could be shown between rupture, increased laxity and poor function. Of particular concern, all post-operative knees had radiographic signs of degenerative change compared with a rate of 39% in the contralateral knees.