Background: Despite being a common orthopedic injury, the optimal management of proximal humeral fractures remains a topic of debate. Although intramedullary nails have been used to treat these fractures, several complications have been reported with older nail devices. We describe our surgical technique and aim to evaluate the early functional and radiological outcomes of displaced Neer's two-to four-part proximal humeral fractures undergoing fixation with a contemporary straight intramedullary nail. Methods: A prospective cohort study of 22 consecutive patients (mean age 55.7 + 18.0) with acute displaced proximal humeral fractures underwent intramedullary nailing (Depuy Synthes MultiLoc Humeral Nail) by a single surgeon in a single institution. According to Neer's classification, 11 had two-part fractures, 9 had three-part fractures, and 2 had four-part fractures. Functional and radiological outcomes, as well as occurrence of complications, were assessed at 12 months postoperatively. Results: The mean Constant-Murley score and American Shoulder and Elbow Surgeons score at 12 months were 75.5 + 12.1 and 81.7 + 6.2, respectively. Mean range of motion was forward flexion 144.3 + 28.4, abduction 141.3 + 30.5, external rotation 58.0 + 13.9, and internal rotation 62.0 + 15.2. Mean visual analog scale score was 1.7 + 0.8. Radiographic fracture union was achieved at a mean of 3 months postop. One patient underwent a second surgery for screw removal due to a proximal screw backing out. No other complications were found in our cohort. Notably, no patients had clinical signs and symptoms of subacromial impingement and/or rotator cuff tear. Conclusion: Our study demonstrated that intramedullary nailing using the contemporary straight nail design is well suited for Neer's two-and three-part proximal humeral fractures, with good early outcomes and low rates of complications. Results for four-part fractures were, however, inferior in our cohort, suggesting that further studies with larger patient numbers are needed to determine the role of intramedullary nailing for four-part fractures.