PURPOSE: To determine the incidence and extent of torsional mal-alignment in patients with tibial shaft fractures treated with closed antegrade intramedullary(IM) nailing. MATERIALS AND METHODS: We measured torsion using CT scanning in 35 patients. Affected tibiae were compared with the normal tibiae. RESULTS: A torsional difference of 8degrees or more found in 22 cases(63%) as compared with the uninjured side. Only 7 of these cases could be clinically detected and only two patients noted the problem. CONCLUSION: Torsional mal-alignment occurs in a significant number of tibial fractures treated by closed IM nailing in spited of careful attention to detail. We recommend that torsional mal-alignment be considered as a likely cause for less than optimal result after treatment of the tibial fractures by closed IM nailing and to investigate this further by performing CT scans.