OBJECTIVE This study introduces an intramedullary nailing technique with external fixation and aims to determine the safest position of Schanz screws for this technique. METHODS Patients undergoing intramedullary nailing were evaluated by computed tomography to assess the anteroposterior (AP) length of the medullary canal and the distance between the posterior cortex and the posterior border of the nail at the level of interest in the proximal and distal tibia. In this cadaveric study, screws were inserted at the level of interest, followed by a determination of the anatomical relationship between inserted screws and nearby neurovascular structures. RESULTS The safe area for inserting Schanz screws in the medial to lateral direction in the proximal tibia was found to be 1.5-4.5 cm distal to the knee joint line on the AP view, 1 cm anterior to the posterior cortex at the distal 4.5 cm level, and ≤ 24 mm from the posterior cortex on the lateral view. In males, the area 1.5-3.0 cm proximal to the tibial plafond and 0.5 cm anterior to the posterior cortex on the lateral view was found to be a safe zone. However, in females, the safe zone was defined as an area 1.5 cm proximal to the tibial plafond and just anterior to the posterior cortex. CONCLUSIONS This study defined the safe zones of Schanz screws for intramedullary nailing with an external fixator. These safe zones would be helpful for external fixation during intramedullary tibia nailing.