Firat Seyfettinoğlu, Hasan Ulaş Oğur, Ümit Tuhanioğlu, Hakan Çiçek, Ahmet Kapukaya Orthopaedics and Traumatology Department, Adana Numune Training and Research Hospital, Adana, Turkey Background: To evaluate the treatment efficacy and complications of the lateral minimally invasive plate osteosynthesis (MIPO) method in geriatric patients with a humerus diaphyseal fracture with proximal extension. Patients and methods: The study included a total of 21 patients (18 females, 3 males; mean age 74±6.3 years, range 65–89 years) who underwent surgery with the lateral MIPO technique for a humerus diaphyseal fracture with proximal extension during the period January 2011 to December 2016. None of the patients had additional injuries and all completed regular follow-up. According to the Arbeitsgemeinschaft für Osteosynthesefragen/Association for the Study of Internal Fixation classification system, the fractures were evaluated as 12C1 in 17 cases and 12C3 in 4 cases. All patients were evaluated radiologically and functionally at 6 months and 1 year. In the follow-up evaluations, the Constant–Murley score and the Quick Disabilities of the Arm, Shoulder, and Hand (Q-DASH) score were used. Results: No non-union, avascular necrosis or infection was seen in any patient. The mean time to union was 15.7 weeks. Impingement syndrome was seen in 2 patients and radial nerve palsy in 2 patients. The mean Constant–Murley score was 70.6±10.2 at 6 months and 84±7.6 at the end of 1 year. The mean Q-DASH score was 38.6±15.1 at 6 months and 21.9±13.1 at the end of 1 year. The increase in the Constant–Murley scores from 6 months to 1 year was statistically significant (p<0.0001). The decrease in the Q-DASH scores between 6 months and 1 year was determined to be statistically significant. In the 2 patients with radial nerve palsy, the functions were seen to completely recover during follow-up. No axillary nerve palsy was seen in any patient. Conclusion: Metadiaphyseal humerus fractures with proximal extension in the elderly can be successfully treated with the lateral MIPO technique. When applied correctly, it is a method with high rates of union and low rates of complications. Keywords: metadiaphyseal fractures of proximal humerus, minimal invasive plating, elderly patients