Abstract The aim of our study is to determine the incidence and extent of torsional malalignment in patients with tibial diaphyseal fractures treated with closed antegrade intramedullary (IM) nailing. We measured torsion using CT scanning in 22 patients. A difference of 8° or more was found in 8 cases (36%) as compared with the uninjured side. Only 2 of these cases could be clinically detected and only one patient noted the problem. We also describe a method of directly calculating torsion from CT images captured on a single film that is easy and does not require any special equipment.