Fourteen patients with acute displaced proximal humerus fractures were treated with a proximal locked antegrade humeral intramedullary nail (Polarus nail). These patients were treated by one surgeon and records were reviewed retrospectively. Clinical outcome measurements included active elevation and external rotation; a functional outcome measure, the Shoulder Pain and Disability Index (SPADI); and complications. Radiographic outcome measures were union, alignment, and presence of avascular necrosis. All 14 fractures went on to clinical and radiographic union. Mean time to union was 4 months (range, 2-9 months). Four patients had postoperative complications. Mean SPADI score was 30 (good) (range, 4-67). There were no cases of postoperative avascular necrosis, and the average radiologic neck/shaft angle was 121 degrees (range 90 degrees -144 degrees ). The proximal locked antegrade humeral intramedullary nail used in the treatment of displaced proximal humerus fractures results in predictable union and good alignment and function.