Background: Humerus shaft fractures are common in orthopaedic practice. The emphasis in treatment has shifted from prolonged immobilisation to early mobilisation and internal fixation when needed for a quicker return to normal function. Internal fixation methods include plate osteosynthesis and intramedullary nailing. This study specifically evaluated the effectiveness of flexible intramedullary nails in treating diaphyseal humeral fractures.Material and methods: Between April 2007 and January 2010, Alexandria University Hospital treated 29 patients (21 males, 8 females) with diaphyseal humeral fractures. Treatment involved closed reduction and percutaneous fixation using two flexible nails. Patients, aged 17 to 65 with a mean age of 32, were included if they did not have pathological fractures, were above 16 years old, and were medically suitable. Causes included pedestrian vehicle accidents (17 cases) and falls or sports-related activities (12 cases). Surgical intervention occurred 1 to 8 days after the injury.Results: Between April 2007 and January 2010, Alexandria University Hospital treated 29 patients (21 males, 8 females) for diaphyseal humeral fractures using closed reduction and percutaneous fixation with two flexible nails. Patients, aged 17 to 65, were monitored for an average of 18 months. Radiographic assessments showed complete union in nineteen fractures within 13 to 21 weeks. One patient experienced non-union but was successfully treated with bone grafting and plating.