Four hundred and eighty-seven total knee arthroplasties were performed by a single surgeon with use of a porous-coated anatomic prosthesis between 1982 and 1989. There were thirty-two clinical failures (7 per cent) due to severe wear of the surfaces of the tibial and patellar polyethylene components. Thirty patients had a revision. The average time to failure of the implant was four and one-half years. The initial clinical symptoms of failure by wear consisted of a painless effusion with a decreased range of motion. Subsequent pain was considered as the criterion for failure necessitating operative intervention. Increased weight and decreased age of the patient and a thinner tibial component were significant predictors of an increased risk of failure (p < 0.01). Examination of retrieved tibial components revealed extensive delamination caused by fracture of the polyethylene at a depth of about one millimeter below the surface. Cracks that had propagated in from the medial and lateral peripheries of the tibial component toward the center of the condyles were also a common finding. It appears that the design of the implant as well as clinical factors (the age and weight of the patient) contributed to the mechanical failure of the polyethylene of these implants.