A Hoffa fracture is an uncommon clinical entity typically seen in adults after high-energy trauma. Nonunion of a Hoffa fracture appears to be even more uncommon. To our knowledge, only three cases of nonunion of a Hoffa fracture have been documented in the literature to date, including two children and one adult. This article presents a case of an adult who had nonunion of a Hoffa fracture for 27 years and was treated by open reduction and internal fixation, and the varus deformity corrected with xenogenous bone graft. An excellent result has been achieved to date. This unusual case reminds us that we cannot neglect the possibility of nonunion of a cancellous bone fracture, especially the Hoffa fractures of the medial femoral condyle if they are treated nonoperatively. It also demonstrates that internal fixation with bone graft is effective, even for the 27-year Hoffa fracture.