In this cadaveric study, the safety and accuracy of a specially designed guide device for the placement of thoracic pedicle screws was investigated in a normal anatomical situation. Five embalmed human cadaveric thoracic spines (T1-12) were used for the study of transpedicular screw placement in the thoracic spine. Overall 120 screws were placed at all thoracic levels. The screws were inserted bilaterally in the thoracic pedicles by using a specially designed guide device. No radiographs or other imaging studies were obtained. Following screw placement, computerized tomography scans were performed to evaluate the accuracy of the pedicle screw positioning. Seven (5.8%) of the screws penetrated the pedicle wall or the vertebral body (VB) cortex. Two screws (1.7%) penetrated the medial wall of the pedicle. Two screws (1.7%) penetrated the lateral wall of the pedicle, and one screw (0.8%) penetrated the lateral wall of the pedicle and the anterior VB cortex simultaneously. Two screws (1.7%) penetrated the anterior VB cortex. Compared with the results of other studies, the findings here indicate that using this device to guide the placement of thoracic pedicle screws can significantly reduce the incidence of pedicle penetration, particularly in the medial wall.