Purpose : The purpose of this study was to compare the postoperative success and stability of arthroscopically assisted anterior cruciate ligament(ACL) reconstructions using the central one third bone patellar tendon bone(BPB) autograft versus a quadrupled semitendinosus/gracilis(ST) autograft in patients with "isolated" ACL tears. Materials & Methods : A strict criteria to identify isolated ACL tears was used which included : no previous surgery, no other ligamentous injury, no history of patellofemoral symptoms, no patellofemoral malalignment, no meniscal pathology, no chondromalacia or chondral injury and no limitation of motion of the injured knee. 30 patients (15 BPB, 15 ST) with a mean age of 27.4 years were available for a mean follow up of 18 months (between 12 months and 26 months). Preoperatively, there was no significant difference between the two groups with respect to age, sex and degree of laxity. Results : Postoperatively, we couldn't find significant differences between the two groups with respect to subjective Lysholm score, objective laxity including Lachman test, pivot shift test and KT-2000 measurements. Mean side to side difference of KT-2000 scores at 20lbs were 1.5mm for the BPB group and 1.4mm for the ST group. Positive Lachman test was found in 26.7% and 33.3% and positive pivot shift was found in 20% and 33.3% of the patients in the BPB and ST groups, respectively. Anterior knee pain (33.3%) was more common in the BPB group. There were 80% of the patients in both groups above nearly normal grade according to the IKDC grade. Conclusions : In patients with "isolated" ACL tears, the overall results, ligamentous stability for the patellar tendon and the quadrupled semitendinosus/gracilis were comparable. We consider that the quadrupled autogenous hamstring tendon is a good alternative substitute in ACL reconstruction together with the bone patellar tendon bone.