Intramedullary nailing is one of the most commonly used surgical treatments for humeral diaphyseal fractures. Once an intramedullary fixation technique has been selected, the choice between antegrade or retrograde approach remains controversial. Forty patients with humeral diaphyseal fracture treated with Seidel antegrade intramedullary nailing through an "danterior deltoid incision" (ADI) were evaluated after an average period of 62 months. Clinical and functional evaluation of the shoulder was performed using the Constant Score. Results were excellent in 33 patients, good in 5 and acceptable in 2. Radiological assessment was performed using antero-posterior (AP) and latero-lateral (LL) radiographs of the humerus and AP and Neer radiographs of the shoulder. Radiographic findings demonstrated good consolidation of all fractures; nail and locking proximal screw malpositioning were detected in 2 cases (2 patients with acceptable results). The positive results obtained for shoulder function correlate with patient age and demonstrate that antegrade intramedullary nailing is a valid option for the treatment of humeral diaphyseal fractures, as long as it is performed through ADI access and with the appropriate surgical technique. Surgical technical errors will lead to functional problems of the shoulder, which in some cases will not be completely eliminated even after nail removal.