Objective To compare partial flexion true sagittal (FS) magnetic resonance (MR) images with extension sagittal oblique (ESO) MR images with regard to delineation of the anterior cruciate ligament (ACL) in the knee. Design: To establish the appropriate degree of flexion of the knee joint, two human cadaveric knee joints were used as a supplementary technique. FS and ESO images then were performed in 17 knees with an intact ACL and six knees with a torn ACL. In 22 of the 23 knees in which the MR diagnosis of intact or torn ACL corresponded to that derived from arthroscopy, the paired MR images were rated by a three-point scale. Results: FS images were rated superior to ESO images in 53%, 41% and 47% of cases with regard to femoral attachment sites, midportions and tibial attachment sites of intact ACLs, respectively. FS images allowed better assessment of disrupted ACLs and residual ligamentous structures. Overall the FS images were either equal to or better than the ESO in the majority of cases. Conclusion: FS images are useful when the ACL is not well visualized in initial ESO images.