A 42-year-old woman presented with right oculomotor, abducens, and trigeminal palsy. Neuroimaging revealed a small lesion in the right cavernous sinus mimicking meningioma. Because the symptoms gradually worsened, the patient underwent an endoscopic endonasal transsphenoidal surgery for tumor biopsy. Histological examination of the surgical specimen revealed adenoid cystic carcinoma (ACC). Before and after the operation, no evidence of other primary lesions could be detected. The patient was treated with stereotactic radiosurgery (SRS). ACC in the cavernous sinus can be difficult to diagnosis before histological confirmation, because it is extremely rare as a primary lesion and resembles a cavernous sinus meningioma on neuroimaging studies. Two years after the first SRS, the tumor recurred along the trigeminal nerve and SRS was performed again. Our study illustrates that in case in which a lesion in the cavernous sinus progresses on neurological and neuroimaging studies, a biopsy should be taken to provide most accurate diagnosis and treatment 1).