A geriatric dog with unilateral, non-painful, facial muscle atrophy presented to Cornell University Hospital for Animals (CURA). Results of the physical and neurological examinations neurolocalize the lesion to the trigeminal nerve. The dog received a diagnostic work-up that included magnetic resonance imaging, cerebral spinal fluid tap, thoracic radiographs, and ultrasound. It was diagnosed as most-likely a peripheral nerve sheath tumor (PNST) of the trigeminal nerve, however lymphoma could not be ruled out as a possibility. Treatment consisted of managing any discomfort with gabapentin and prednisone as well as addressing eye ulceration concerns.