Hoffa fractures are unstable intra-articular fractures of the femoral condyle that occur in the coronal plane.Insufficient anatomical reduction and internal fixation may lead to non-union or malunion. A 39-year-old man was involved in a traffic accident while riding a motorcycle and was diagnosed with left Hoffa fracture and avulsion fracture of the femoral attachment of the medial collateral ligament. Open reduction and internal fixation were performed 5 days after injury. The patient experienced intermittent knee pain, joint contracture and deformity, and attended our hospital for further treatment 18 months after surgery. CT revealed depression and malunion of the posterior aspect of the lateral femoral condyle, and weight-bearing X-ray showed valgus deformity due to malunion. Distal femoral osteotomy (DFO) was performed and good functional and radiographic results were obtained. This report suggests that DFO is a reasonable treatment for young patients suffering from malalignment due to malunited Hoffa fracture.