Authors have analysed 20 cases of the humeral shaft fractures treated with closed intramedullary nailing at the department of orthopedic surgery, Lee-Rha general hospital from June 1991 to December 1993 with minimal 1 year follow up. The results were as follows

1. In the 20 cases, the age between 20 and 40 years old was taken place 60% and the most common cause of injury was traffic accident (75%)

2. It was worthwhile to define the relationship between union time and Winquist-Hansen classification which used in femoral shaft fracture. And the average bone union time was 8 weeks except 3 cases, especially delayed union was found in type 3 of Winquist-Hansen classification. But 2 cases were united after 9 monthes follow up without secondary procedure.

3. Problem in Seidel nailing was flilure of expansion of distal portion and in Russel-Taylor nailing was impairement of internal rotation of shoulder and delayed union due to iatrogenic distraction at the fracture level during operation.

In according to the above results to treat the humeral shaft fracture, closed intramedullary inter-locking nailing was satisfactory enough to obtain bone union and early recovery of shoulder motion. Also, the Winquist-Hansen classification is useful guide to find the bone union time in the treatment of humeral shaft fracture with interlocking nail.