We present a new surgical technique of anterior cruciate ligament (ACL) augmentation using autogenous hamstring tendons or allogenic fascia lata under arthroscopy for patients in whom considerable ACL remnants with mechanoreceptors are preserved. We review the clinical results of 40 patients who underwent this ACL augmentation, as assessed by manual instability tests, KT-2000 knee arthrometer, Lysholm and Gillquist score, joint position sense and magnetic resonance imaging (MRI), and compare them with those of ACL reconstruction. The side-to-side differences of anterior displacement measured by the KT-2000 knee arthrometer at 30 lbs, an average of 5.3 +/- 2.6 mm preoperatively, was significantly improved to an average of 0.7 +/- 1.8 mm in the augmentation group, while an average of 6.0 +/- 2.4 mm was improved to 1.8 +/- 2.1 mm in the reconstruction group. There was no statistically significant difference between the preoperative values in the two groups, but the postoperative values of the augmentation group were significantly less than those of the reconstruction group. The ratio of anterior terminal stiffness of the augmentation group was 1.2 +/- 1.8, and that of the ACL reconstruction group was 0.7 +/- 0.4. This was a statistically significant difference (P < 0.05). Thus, as for the KT-2000 knee arthrometer, the ACL augmentation group showed significantly better anteroposterior stability and terminal stiffness than the ACL reconstruction group. The final inaccuracy of joint position sense of the augmentation group was 0.7 degrees +/- 0.7 degrees, while that of the reconstruction group was 1.7 degrees +/- 1.2 degrees indicating a significant difference (P < 0.05). This study demonstrates that ACL augmentation, which can preserve ACL remnants with mechanoreceptors, is superior to ACL reconstruction from the viewpoint of position sense and joint stability.