Objective: To introduce the experience of treating nonunions of humeral fractures with interlocking intramed-ullary nailing. Methods: Twelve patients with humeral nonunions were treated with interlocking intramedullary nailing. The time interval between trauma and surgery was 10.5 months on average. Open reduction with anterograde approach was performed. Axial compression was specially applied to the fracture site with humeral nail holder after insertion of distal locked screws. Iliac bone grafting was added. Results: The average follow-up period was 21 months (ranging 9-51 months). All patients achieved osseous union 5.8 months after treatment on average. Eleven patients had good functions of the shoulder joints and the upper extremities. No patient experienced any permanent neuro-logical deficit. Refracture of the original ununited region occurred in one patient after removal of the internal fixator one year later, but union was achieved after closed re-intramedullary nailing fixation. Conclusion: Humeral interlocking intramedullary nail-ing is an effective alternative treatment for humeral nonunion.