Twenty-four proximal humeral fractures were treated by surgical internal fixation with a locked antegrade intramedullary nail. The purpose of this paper was to assess the clinical outcomes of proximal epiphyseal and diaphyseal humeral fractures treated with an antegrade humeral nail implanted after an interval rotator split. We treated six proximal epiphyseal fractures and seven bifocal fractures of the epiphysis and shaft and eleven diaphyseal fractures. The mean follow-up was 23 months (range 12 to 34 months). Twenty patients were available for follow-up. All but two fractures progressed to healing. The Mean Constant score was 80%, Relative Constant score was 95.5%. We divided the clinical outcomes by fracture pattern to define the best surgical indication. There were good clinical outcomes in all three groups, but the clinical score was highest in the shaft fracture group. An intramedullary antegrade nail inserted through the interval rotator without penetrating the rotator cuff had a good clinical outcome and with certain fracture types can be an effective and satisfactory device.