PURPOSE: To evaluate the radiographic and clinical outcomes of patients with displaced proximal humerus fractures (two-part and three-part) treated with the Polarus interlocking nail, comparing their fractures types. MATERIALS AND METHODS: There were 22 patients with displaced proximal humerus fractures. There were 10 surgical neck (SN) and 1 anatomical neck (AN) two-part fractures and 10 greater tuberosity/surgical neck (GT/SN) and 1 GT/AN three-part fractures. All patients were surgically treated solely with the Polarus interlocking nail using a closed technique. Functional assessment was obtained using the American Shoulder and Elbow Surgeons (ASES) score, which grade outcomes as excellent (>75), satisfactory (50~75), poor (<50) results. Radiographic outcome measurements included fracture alignment (neck-shaft angle), loosening of screw, fixation and hardware failure, and malunion and nonunion. RESULTS: Overall, the average ASES score was 80.2 (range 46.0 to 98.0). There were 15/22 (68.2%) excellent, 6/22 (27.3%) satisfactory, and 1/22 (4.5%) poor results. All shoulders healed radiographically without evidence of avascular necrosis of the humeral head. When comparing patients with two-part fractures (n=11) with patients having three-part fractures (n=11), there were statistically significant differences with ASES outcome measures (p<0.05). But, there were no statistically significant differences in age-related analysis (p>0.05). CONCLUSION: Both displaced two-part fractures and three-part GT/SN fractures can have above satisfactory functional and radiographic outcomes with the Polarus interlocking nail using a closed technique. Even though displaced three-part GT/SN fractures in elderly osteopenic patients (>60 years), we treated successfully with the Polarus interlocking nail.