[Purpose] To compare the reliability of goniometric measurements of knee flexion obtained in three different body positions of patients with total knee arthroplasty (TKA). [Subjects] The knees ( 15 1) of 92 TKA patients were the subjects of this study. [Methods] The range of flexion was measured at three instances: preoperatively, postoperative fifth day and at the time of discharge by universal goniometer measurement with the patient positioned in the supine, prone and sitting positions. [Results] There were no significant differences between the range of motion measurements in the three testing positions at the three instances. Also, the results from the three different testing positions were highly correlated (r>0.80). [Conclusion] The results of this study indicate that the position of the patient during the evaluation of range of knee flexion does not affect the results and that the three different body positions can be used interchangeably.