Certain practical parameters are needed for progres1s measurements in osteoarthritis (OA) patients. In the present study, joint spaces were measured on the knee radiographs of 21 OA patients and 20 healthy subjects, which were taken both in stand up and supine positions, and were compared. Bilateral joint spaces of the OA patients were found narrowed when compared with the control group. In addition, the comparison among each group showed that bilateral tibiofemoral joint spaces on the radiographs taken in stand up position were narrower than the radiographs taken in supine position, and narrowing in medial joint space is greater (p<0.001) and Lequesne knee severity index, body mass index and joint spaces were all statistically correlated with each other (p<0.001). As a result, it has been thought that quantitative measurement methods are more sensitive, because of being slow progres. Especially, the evaluation of the medial tibiofemoral joint space on radiographs taken in stand up position is more precious in evaluation of both the progres and the outcome.