Investigations which began in 1968 have culminated in a knee arthroplasty which can now be confidently used to treat most patients with arthritic knee deformities. Our earlier studies showed that a prosthetic knee arthroplasty must be reliably aligned and stabilized in extension, that patellar pain and polyethelene wear were significant potential problems and that loosening and sinkage of the tibial component must be avoided. Our present knee prosthesis and instrumentation if properly used should avoid these pitfalls. Beginning in January 1977 we performed 84 knee arthroplasties utilizing the present design. A series of 79 knees has been available for our computer-assisted review; 46 patients had a diagnosis of inflammatory arthritis and 29 had primary osteoarthrosis: 22 knees had been previously operated upon. Although all femoral components were fixed with polymethylmethacrylate, the tibial components were completely cemented in 21 knees, partially cemented in 20, and no cement was used in 38 cases. In these latter knees special pegs provided a mechanical interlock with the tibia for fixation. Thirty-six patellae were replaced, of which 11 were fixed with a similar interlocking peg. The arthroplasties failed in 8 patients. Of the remainder, 90% of knees had acceptable pain relief and all but 4 patients were able to walk outdoors. Flexion to 90 degrees or more was achieved in 85% of the knees. Only 2 patients had unacceptable alignment. To date we feel that with the use of this improved prosthesis, in conjunction with the instruments which allow proper placement of the prosthesis, the majority of arthritic knees can be successfully corrected. However, further careful long-term follow-up studies must continue.