Nineteen cases out of over 100 cases which had been reconstructed the deficient anterior cruciate ligament(ACL) by the bone-patellar tendon-bone(BPTB) autograft 12 months before or more(mean 15.8 months) were evaluated during the second-look arthroscopy. Before the second-look, the patients were evaluated the clinical results of ACL reconstruction by the Müller's knee rating score and the radiographical results by the lateral roentgenography of the fully extended knees. The location of the center of tibial tunnel from the anterior end of the line of the tibial plateau was 35.2%(range, 22 to 47%) on average. The average intercondylar roof angle was 36.6 degrees(range, 28 to 45 degrees). The mean percentage of roof impingement was -13.5%(range, −55 to +23% ; the negative value implies no impingement, while the positive value suggests the presence of impingement). During the second-look arthroscopy the ACL graft had one or more following features: nearly normal appearance, incomplete synovial coverage, partially torn fibers at the femoral tunnel site, parallel fragmentation with cyclops lesion and radiographically impingement without the damage of the ACL graft. The biopsy specimen had been achieved form the nearly normal ACL graft during the second-look arthroscopy and light microscopic findings showed dense collagen fibers and the spindle-shaped fibroblasts with relatively regular arrangement(H&E, ×200). The electro-microscopic findings showed: (1) The fibroblast had prominent indented nucleus and numerous rough endoplasmic reticulum(×10200). (2) The longitudinal sections of extracellular collagen fibrils showed type I collagen banding pattern(×50000).