Deformities of the lower extremities are often a combination of angular and rotational components. The rotational component of combined deformities may be difficult to measure using plain radiography. Based on the current study, the computed tomography rotational malalignment test was developed. Evaluation of lower extremity alignment was done on 56 patients. Rotational malalignment was diagnosed in 14 limbs of nine patients. In all patients, correction of angular and rotational deformities was done simultaneously using an Ilizarov external fixator. The frame included a standard angular distraction system and a derotation block interconnected via an additional empty ring. In all cases, successful correction of angular and rotational deformities was achieved. The pain was eliminated in all seven patients having preexisting chronic joint pain. There were no cases of deep infection or nonunion. This simple and reliable method allowed precise analysis of the deformity in the transverse plane. Preoperative frame construction incorporating the derotational module decreased the time of the operation and allowed one-stage correction of rotational and angular deformities without additional manipulations.