Facial nerve paralysis (FNP) can occur following trauma, with a small number of these patients requiring facial nerve decompression (FND) to aid recovery. The authors shared their experience in decompressing the facial nerve for persistent severe FNP via a transmastoid approach. They focused on patients with persistent House-Brackmann (HB) grade V or VI weakness more than one month after injury, with no observable recovery despite systemic corticosteroid treatment. All patients underwent electromyography (EMG) and high-resolution computed tomography (CT) scan. Fracture line or bony spur involving the fallopian canal and EMG showing total or near total axonal degeneration were deemed an indication for surgery. Thirteen patients underwent FND between 2010 and 2017 with the surgery performed between one and three months post trauma. The technique involved a combined approach of posterior and anterior tympanotomy to identify and decompress the facial nerve 180 degrees. The ossicular chain was not disturbed and, in cases where the incus was removed for access, it was either restored to its original position and fixed with bone cement or interposed. Ten patients had injuries around the perigeniculate region, and the majority of patients had bony spicules within the fallopian canal. The authors did not find any cases of complete facial nerve transection. At one year post FND, there was improvement in 12 out of 13 patients, with the patients scoring HB grade three or better. There was no correlation between timing of surgery and the likelihood of improvement. Transmastoid FND appears to be a safe and effective treatment of persistent severe facial weakness following trauma. The findings that FND surgery can lead to improved facial function up to three months following injury are useful as many patients with skull base fracture also suffer from multiple injuries, necessitating a stay in the intensive care unit, making immediate assessment of the facial function difficult. Careful patient selection is needed as well to determine the site of facial nerve injury prior to performing transmastoid FND.