The results of 94 Macintosh arthroplasties in 71 patients with rheumatoid arthritis were examined by an independent assessor, a mean of 47.9 months post-operatively. The results were graded as good, fair or poor on the basis of the patient′s opinion, functional status and joint examination. There were 49 good results, 23 fair and 22 poor of whom 10 had been converted to total knee replacements. Better results were achieved with a single medial or lateral prosthesis even in the presence of bicompartmental disease. A minimum five-year follow-up in 28 cases showed the same results as the whole group, suggesting that there is little deterioration with time. It is concluded that Macintosh arthroplasty remains a useful procedure, has a low incidence of complications and can be converted to knee replacement. It remains difficult to predict factors likely to produce poor results.