Early and late results of the GUEPAR hinge knee prosthesis were evaluated on a series of 184 operations performed before January 1st, 1974. There were 3 immediate deaths and 26 before 5years. Nineteen prostheses were removed. One hundred and twenty-six knees had degenerative osteoarthritis, 52 rheumatoid arthritis. Twenty-two had been operated on before. Patellar displacement, present in 27% of the cases, was the most frequent cause of complaint: pain or instability, proportional to the severity of displacement, made re-operation necessary in 10% of the patients. Addition of a patellar prosthesis was the most successful treatment as far as pain is concerned: it is probably advisable as a primary procedure. Deep infections occurred in 8.3% of the cases, infrequently after 2years. Healing was obtained in all cases either by revision or by removal and arthrodesis: but functional results were poor except when fusion was achieved, in half of the cases of arthrodesis. Loosening occurred in 16% of the cases, mainly as a consequence of inadequate technique. It was frequently tolerated: re-operation was necessary in 6% of the total. Late functional results were evaluated in 99 cases with a follow-up of 5 to 8years. Apart from loosening, the results did not deteriorate. Sixty percent were evaluated as excellent or good, 29% fair, and 11% poor. In consideration of these results, the choice of this prosthesis should be limited to special cases. To prevent complications, the use of a patellar prosthesis, of reinforced models and of cementing under pressure is advisable.