The aim of this study was to investigate the biomechanical characteristics of anterior tibial translation (ATT) in anterior cruciate ligament (ACL)-deficient or -reconstructed knees with active and isokinetic knee extension exercise. Forty-nine patients with unilateral isolated ACL-deficient knees were enrolled. Follow-up examinations were carried out at a mean of 24 months postoperatively. An electrogoniometer system was applied to compare the amount of ATT in ACL-deficient and -reconstructed knees. For both active and isokinetic knee extension, the mean ATT of ACL-deficient knees was considerably greater than that for the normal side, within a range of flexion 0 degrees -70 degrees and 0 degrees -60 degrees, respectively. In contrast, no mean ATT differences were seen during both active and isokinetic exercise from 90 degrees to 0 degrees at follow-up. Within a range of flexion between 50 degrees and 70 degrees, the side-to-side difference in ATT with active knee extension was significantly greater than that with isokinetic extension in ACL-reconstructed knees. These results suggest that the amount of ATT is significantly improved with both active and isokinetic exercise, postoperatively. However, postoperative ATT with isokinetic extension is smaller than that with active knee extension from 50 degrees to 70 degrees.