The arthroscopic reconstruction of the anterior cruciate ligament requires the partial removal of the patellar tendon. US potentials in the assessment of residual patellar tendon after bone-tendon-bone removal were compared with those of CT and clinics. Mechanical resistance reduction of the residual tendon may be caused by removal modalities and size. This work was aimed at investigating the morphologic US patterns indicating "stability" of the operated tendon, which is mandatory for a risk-free functional recovery. Twenty patients were submitted to US of the operated tendon with contralateral comparison. In each patient tendon thickness and structure in the site of removal were studied, especially aiming at demonstrating diffuse or focal alterations of echogenicity. Middle third thickness and new tissue echostructure are fundamental US variables to define residual tendon "stability". The authors describe some US patterns of the surgical tendon to be considered as normal and not abnormal findings, provided that US be performed at least two months after surgery.