After reconstruction of anterior cruciate ligament, increased idameter of femoral or tibia1 bone tunnel has been obsened on plain radiogram. The etiology of radiographic tunnel enlargement is not well understood and the significance of this tunnel enlargement is unknown. This retrospective study reviewed tibial tunnel diameter in 34 cases of anterior cruciate ligament reconstructions. And we evaluated the correlation between the tibial tunnel enlargement and the position of screw fixation, instability, choice of graft, and clinical results at 1 year postoperatively. AII operation was per formed using a single incision technique. After 3 or 4 months and one year after operation, the diameter of tibial tunnel was measured with digital caliper on the plain radiogram. Tibial tunnel sclerotic margins were measured in the level Of medial tibial plateau on the lateral view of knee. Average tunnel enlargement of 3 allografts was 1.62mm and that of 15 autografts was 2.03mm. No significant difference was seen in KT-10000 arthrometer measurements between enlarged group (amount of enlage-ent >+1 S.D) and not-enlarged group (less than +1 S.D). No coelation was present between the increased tunnel diameter and Lysholm score. Cases with 10mm or more vertical distance between the most proximal point of tihial interference screw and the level of m4eial tibial plateau had average 1.15mm tibial tunnel enlargement and cases with less than 10mm vertical distance ha & I average 2.52mm tibial tunne] enlargement;the difference was not significant (P>0.05). The tibial tunnel enlargement was not correlated with position of screw, clinical results, stability of knee. The tibial tunnel enlargement was not caused hy only mechanical factor such as motion of intra-tunnel portion of graft-tendon.