Objective To study the clinical value of using a four-point method (FP) in measuring joint angles.Method Methods Twenty-five subjects without knee dysfunction were studied.Every knee joint was tested in extension,below 90° of flexion and above 90° of flexion with the traditional three-point method (TP) and the new four-point method.X-rays were taken as a gold standard measurement.The reliability and validity were analyzed using Bland-Altman plots,which can yield 95% limits of agreement (LOA).Results (1) The joint axis centers moved with changes in joint angle.(2) The 95% LOA of inter-tester reliability was (-5.0,2.7) with the FP and (-6.5,4.4) with the TP.The 95% LOAs of intra-tester reliability were (-3.6,4.0) for tester A and (-4.1,4.8) for tester B with the FP,while (-5.0,6.4) for tester A and (-6.1,5.8) for tester B with the TP.(3) The 95% LOAs in the three positions were (3.5,2.6) in extension,(-3.3,3.6) in mild flexion and (-1.9,5.7) in greater flexion with the FP,and ( 6.8,1.1),(-4.0,7.1) and (0,8.5) with the TP.Conclusions The FP gives better reliability and validity than the TP in joint angle measurement.