Twenty-six severely deformed patients with prosthetic arthroplasty of both hips and both knees because of rheumatoid arthritis (16), juvenile rheumatoid arthritis (6), ankylosing spondylitis (2), osteoarthritis (1), and inflammatory arthritis, cause unknown (1), were followed for a mean of 6.8 years. Severe pain was the primary indication for surgery, and consistent and substantial pain relief was achieved. Most patients also had limited ambulatory and functional improvement. Computer analysis showed that this improvement was related only to preoperative walking and function and a combined hip and knee flexion of at least 190 degrees. All other parameters had no correlation with walking and function improvement. Of the 104 arthroplasties (52 hips and 52 knees), six implants (4 hips and 2 knees) in two patients failed and another seven implants (2 hips and 5 knees) in five patients were revised. Of the remaining 91 implants, 89 were clinically stable, and only two hip implants in two patients appeared destined for revision. However, when radiographic review was included, nine acetabular components, three THA femoral components, and five tibial components in 12 patients had some evidence of impending aseptic loosening, despite low patient activity levels.