This study was designed to analyze anteroposterior and rotational movement of femoral condyles during knee flexion from 15° to 90° using magnetic resonance imaging. After a pilot study, scans were made in 10 healthy male Japanese volunteers. When centers of the circular profiles of posterior femoral condyles were used as reference points, the medial and lateral femoral condyles displaced posteriorly 1.9 ± 0.8 mm and 2.3 ± 0.5 mm, respectively (mean ± standard error). Duplicate examinations on two separate occasions revealed the accuracy of this procedure was in the range of 1 to 2 mm. These results have confirmed that femoral rollback occurs in the unloaded normal knee during flexion from 15° to 90°, but its magnitude is small (2 mm). The results obtained in this in vivo measurement of anteroposterior movement of the femoral condyles have relevance for total knee replacement design.