PURPOSE: To evaluate the postoperative changes occurring in the patellar tendon after reconstruction of the anterior cruciate ligament (ACL) using the central one-third of the patellar tendon together with patellar and tibial bony plugs. MATERIALS AND METHODS: Ten patients with ACL injury underwent sagittal and coronal T1-weighted MR imaging of both postoperative and normal knee joints. In all cases, reconstruction of the ACL was performed using the central one-third of the patellar tendon, together with patellar and tibial bony plugs. During the follow-up period of 6-27 months, patient were clinically stable. We compared the length, signal intensity and contour of both patellar tendons, as seen on MR images. RESULTS: No defects was found in harvested patellar tendons, and MR images showed high signal intensity within harvested tendons in six of the ten patients. In seven of ten, patellar tendons had irregular margins and were poorly delineated from adjacent tissue. The mean length of patellar tendons was 44.2+/-2.9 mm in normal knee and 43.9+/-3.1mm in postoperative knee, while their mean thickness in postoperative knee, measured at mid-portion, averaged 4.3+/-1.2 mm. There were no statistically significant differences (p>0.05). The greatest mean thickness of patellar tendon was 6.9+/-1.2 mm and 4.3+/-0.5mm in normal and postoperative knee, respectively. Thus, on average, postoperative patellar tendon was 161% thicker than normal tendon (p<0.05). CONCLUSION: In clinically stable patients, patellar tendons after graft harvesting had a higher signal intensity, worse-defined margins and a greater thickness than normal. We suggest that these are the normal postoperative findings.