We have treated the open tibia shaft fractures, especially Gustilo type II, with unreamed interlocking intramedullary nail. In cases combined with soft tissue damage around fracture site, maintaining rigid internal fixation and preserving endoosteal blood supply is important in union of fracture and soft tissue healing. We have analyzed 18 cases of Gustilo type II open tibial shaft fractures managed with intramedullary nailing without reaming since 1991, the follow-up period was average 22 months. Most of the fractures were the result of moderate to high-energy trauma. In all 18 cases, nails were inserted via closed method. Static interlocking nailing was used in all cases. In 16 cases, union of the fracture was achieved from 16 to 25 weeks(average 23 weeks). In the other 2 cases, union was achieved in 7 months. There was no serious postoperative complication except one skin infection with skin defect managed by skin flap and one failure of the interlocking screw. These results are comparable with those obtained from other forms of fixation, including immobilization with a cast, reamed intramedullary nailing, and external fixation.