AIM:Pedicle screw instrumentation is widely used in the lumbar spine as a means of stabilization to enhance arthrodesis and has gained acceptance in the thoracic spine in recent years. The purposes of this study were to determine the incidence of screw misplacement, complications, the accuracy and usefulness of CT scan in evaluation of pedicle screw placement. MATeRIAL and MeTHodS: Postoperative CT was performed in all 53 cases to evaluate implant position within first month after surgery. The CT scans were obtained with 2-mm axial slices of the instrumented levels. These images were then inspected for evidence of pedicle violation. ReSULTS: In assessing 247 pedicle screws inserted in 53 patients, lateral screw misplacement was observed in 59 screws (67.82%) and medial pedicle wall violation in 28 screws (32.18%). Of the 87 misplaced screws, 41 cases were classified as minor (cortical perforation ≤ 2 mm), 41 cases as moderate (2.1-4 mm), and 5 cases as severe penetration (> 4 mm).Nerve root injury with radicular pain and neurological deficits was observed in 8 patients with malpositioned screws (15.09% of all patients). CoNCLUSIoN: Pedicle screw placement is a technically demanding procedure with a high complication rate. Fortunately, most complications are not severe.