Adult humeral shaft fractures are associated with primary radial nerve palsy in up to 18% of cases. The purpose of this study was to assess the influence of injury mechanism, fracture type, and treatment on nerve recovery in patients with humeral shaft fractures and primary nerve palsy. Data of fifty patients (age-43.5 ± 21.3; female: male-1:1.8) with humeral shaft fractures and concomitant grade I-II primary radial nerve palsy, who underwent either open reduction and internal fixation (ORIF) or intramedullary nailing at an academic level I trauma center between 1994 and 2013, were evaluated. Factors potentially influencing the time to onset of recovery or full nerve recovery (injury mechanism, fracture type, fracture location and treatment) were analyzed in detail. Thirty patients were treated with ORIF and twenty patients with closed unreamed intramedullary nailing of the humeral shaft, respectively. The mean time to onset of recovery was 10.5 ± 3.4 weeks (2-17 weeks). Twenty-six (52%) patients reported significant clinical improvement within the first 12 weeks. Mean time to full recovery was 26.8 ± 8.9 weeks (4-52 weeks). Twenty-five (50%) patients regained full manual strength within the first six months following the injury. Forty-nine (98%) patients regained full manual strength within the first 52 weeks. Trauma mechanism, fracture type, fracture location, and treatment modality did not influence the time to onset of nerve recovery or time to full recovery following humeral shaft fractures with grade I-II primary radial nerve palsy.