Locking plate fixation of proximal humeral fractures improves biomechanical stability. It has expanded the indications of traditional open reduction internal fixation and become increasingly common for treating unstable, displaced proximal humeral fractures. Despite improved stability it is unclear whether these improve function and if so for which patients. We therefore determined patient function after a locked plating technique for the treatment of unstable proximal humeral fractures based on age, time, fracture pattern, and associated injures. We retrospectively reviewed 66 patients with 69 proximal humeral fractures treated with a locked proximal humeral plating technique from 2002-2006 using prospectively gathered data. Function was measured using the Short Musculoskeletal Function Assessment (SMFA), Disability of the Arm, Shoulder, and Hand (DASH), and SF-36 at 6, 12, and 24months. Fracture healing was determined radiographically and complication rates were determined from the medical records. At 2years, DASH scores were 26.5 and 37.4 for isolated and polytrauma patients, respectively. For age differences, DASH scores were 33.1 and 28.9 for ages younger than 60 and 60years old or older, respectively. At 2years, SMFA scores were higher (worse) in older compared with younger patients. Function, but not bother continues to improve in younger patients up to 2years. More severe fracture patterns performed worse in all SMFA indices at 2years. Polytrauma patients consistently experienced worse mobility than isolated injury patients at each time interval. With locked plating of unstable proximal humeral fractures, older patients function as well as younger patients; improvement continues until 1year postoperatively, the Neer fracture classification differentiates function, and polytrauma patients perform worse clinically. Long-term functional deficits persist. Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.