This study retrospectively evaluated the effectiveness of an open reduction and internal fixation of a tension band wiring technique for treating displaced or unstable comminuted distal ulnar shaft fractures without a radial fracture. Ten patients were treated for an isolated distal ulnar shaft fracture. There were 6 cases of a fracture 2.5 cm below the lower end of the ulna, and 4 cases with the fracture being 2.5 cm to 5 cm away from the lower end of the ulna. The authors classified the fractures of the distal ulnar into 3 types: a type I-simple fracture, a type II-comminuted fracture without a distal radioulnar joint (DRUJ) involvement, and a type III-comminuted fracture with DRUJ involvement. There were 3 cases of a type I fracture, 4 of type II and 3 of type III. The open reduction and internal fixation using tension band wiring were performed in 10 of these cases. After the operation, the wrist was placed in a cast for six weeks before active movement was allowed. The clinical results were excellent in 7 cases, good in 2 and poor in 1. In conclusion, tension band wiring surgery is recommended for treating an isolated distal ulnar with unreduced displaced fractures, in a comminuted fracture that cannot be maintained by a closed reduction and when there is the potential encroachment of fracture fragments in the DRUJ.