Background: Proximal radial nerve lesions located between the brachial plexus and its division into the superficial and deep branches are rare but severe injuries. The majority of these lesions occur in association with humerus fractures, directly during trauma or later during osteosynthesis for fracture treatment. Diagnostics and surgical interventions are often delayed. The best type of surgical treatment and the outcome to be expected often is uncertain. Methods: Twelve patients with proximal radial nerve lesions due to trauma or prior surgery were included in this study and underwent neurolysis (n = 6) and sural nerve graft interposition (n = 6). Retrospective analysis of the collected patient data was performed and the postoperative course was systematically evaluated. The Disabilities of the Arm, Shoulder, and Hand (DASH) and the LSUHS (Louisiana State University Health Sciences) scores were used to determine regeneration after surgery. Comparison between the patients’ and calculated normative DASH scores was performed. Results: All patients had a traumatically or iatrogenically induced proximal radial nerve lesion and underwent secondary treatments. The average time from radial nerve lesion occurrence to surgical intervention was approximately four months (1.5–10 months). Eight patients (66.67%) had a humeral fracture. During follow up, no statistically significant difference between the calculated normative and the patients’ DASH scores was observed. The LSUHS scores were at least satisfactory. Conclusions: Neurolysis or sural nerve graft interposition performed within a specific period of time are the primary treatment options for radial nerve lesions. They should be performed depending on the lesion type. Regeneration to a satisfactory degree was observed in all patients, and the majority achieved full recovery of sensory and motor functions. This was the first study to highlight the efficiency of neurolysis and sural nerve graft interposition as secondary treatment interventions, especially for radial nerve lesions.