Thirteen patients who had had sixteen total knee arthroplasties for pagetic gonarthrosis were followed for a mean of seven years (range, two to fifteen years). Involvement of the femur or tibia with Paget disease was associated with multiple technical difficulties at operation and with a final position in suboptimum varus or valgus alignment (ten limbs) or suboptimum alignment of the mechanical axis (nine limbs). The presence of bone with Paget disease did not affect the amount of blood lost during the operation, the postoperative course, or the rate of loosening of the prostheses. At the most recent evaluation, nine patients had no pain, three had mild pain, and one had moderate pain. The mean Knee Society pain score improved from 42 points preoperatively to 88 points and the mean functional score, from 33 to 86 points.