Eighty-one patients treated by patellectomy for osteoarthritis have been reviewed. Eighty-seven knees were examined with a mean follow-up period of six and a half years. Clinical and radiological assessment was carried out and the results have been analysed. A good result was achieved in 53 per cent, a fair result in 26 per cent and a poor result in 21 per cent. The overall result did not deteriorate significantly with time and the radiological appearance of the tibiofemoral joint deteriorated minimally. Pain before operation, radiological changes at the patellofemoral and tibiofemoral joints and the duration of immobilisation after operation were analysed against the end-result. The only factor before operation that indicated a good prognosis was a minimal radiological change at the tibiofemoral joint. Immobilisation for at least three weeks after operation appeared to be beneficial.