The purpose of our study was to evaluate the interest of passive motion rehabilitation with an automatic device. Our protocol has been made of 120 TKA performed in the same surgical department between february 1987 to June 1990. We draw lots, a group "RC" with usual rehabilitation program and a second group "AM" with the same program added with passive motion two hours per day. The passive motion device was Toronto Mobilimb. Passive range of motion (ROM) of flexion and extension, pain level, deep venous thrombosis existence, volume of blood postop drainage, mobilisation under anaesthesia, device tolerance were studied. The results showed a flexion ROM average of 86.7 degrees in the RC group at discharge and 90 degrees in the AM group. This difference is statistically significant and evokes the efficacy of passive motion. At the term of one year postop, the flexion averages reaches 108 degrees in both groups. The extension lag falls from 8.2 degrees and 9.2 degrees average in AM and RC group at discharge to 3 degrees and 3.7 degrees in the same groups at one year. The mean of blood postop drainage by suction was very different in the RC group than AM group (1149ml-968ml). In conclusion, we can say that passive motion device is useful to reach enough flexion in the first days after surgical day and may give some comfort. In our experience the classical rehabilitation program with physiotherapist must be continued.