The patient was a forty-four years old female. She had sore throat and left side neck swelling. She was diagnosed as having a left peritonsillar abscess and underwent the incisional drainage at another hospital. Following the drainage, her symptoms were temporarily improved. However, the neck swelling and sore throat were persisted, and she was referred to our hospital. Blood examination showed mild inflammation. The cervical CT and MRI revealed a cystic lesion in the left parapharyngeal space. We suspected a brachiogenic cyst or neurilemmoma, and performed surgical intervention. The cystic lesion was located at the dorsal side of the internal and external carotid arteries, and did not show continuity with the vagal, accessory, hypoglossal, or sympathetic nerve fibers. Histopathological examination showed that the wall of the cyst was composed of squamous epithelium and lymphoid follicles had formed. Thus, we diagnosed a Bailey type-IV brachiogenic cyst.