Despite recent advances in operative techniques, internal fixation of (3- and 4-part) displaced proximal humeral fractures in elderly patients with osteoporotic bone remains controversial, sometimes followed by poor results. The aim of the present study was to evaluate outcomes of internal fixation with locking plate of multi-fragment proximal humeral fractures in elderly patients. The study cohort comprised 59 consecutive patients (mean age 70.1) with 3- and 4-part fractures who had undergone open reduction and internal fixation with locked plate at Sestre milosrdnice University Hospital Center in Zagreb, Croatia. All patients were invited for follow-up examinations and underwent standard x-ray examination preoperatively to assess fracture pattern in the operating theatre as well as at 6 weeks, 3 and 6 months, 1 year, and then annually after surgery to assess fracture healing or complications. Clinical outcomes were measured by constant score. Patients were followed-up for 14 to 36 months. The overall complication rate was 27.1%. The mean constant score at 1-year follow-up was 70.2 points for 3-part fractures vs. 64.2 for 4-part fractures (p < 0.0001). In conclusion, despite a relatively high overall complication rate, internal fixation with locking plate provided moderate to good functional results in the treatment of osteoporotic complex proximal humeral fractures.