An 88-year-old man presented with Rathke's cleft cyst (RCC) manifesting as complete cavernous sinus syndrome. He had no headache, endocrinological symptom, or blood abnormality. Neuroimaging revealed a cystic intrasellar lesion with lateral extension. The patient underwent surgery by a transsphenoidal approach. Histological examination revealed squamous and cuboidal epithelium. The diagnosis was RCC. RCC is rarely symptomatic, but enlargement and compression of the surrounding structures usually causes headache, visual field defects, or symptoms of pituitary dysfunction. The present case shows that RCC may manifest as complete cavernous sinus syndrome.