Isolated spinal accessory nerve (SAN) palsy is a well-recognized complication of surgical prodecures in the posterior triangle of the neck. Various rare etiological factors were also described. Whatever the etiology, the typical clinical features of SAN palsy can be listed as atrophy/weakness of the trapezius muscle and moderate winging of the scapula. It is imperative to promptly diagnose this condition in the early stage to avoid long-term impairment and to have a better functional outcome. Herein, we present a patient with a diagnosis of spontaneous spinal accessory nerve palsy, which was rarely reported in the relevant literature.