Therapeutic management of brain tumors is based on accurate knowledge of their size, location and histologic type. Stereotaxic cytology under CT guidance has been applied to the investigation of brain tumors, especially in the sellar turcica, third ventricle, and pineal regions. In the present case, the tumor protruded into the nasal cavity, so we were able to get cytologic material via fine needle aspiration. Although pituitary adenoma is not an unsual tumor, there have been few reports about its cytologic features. We present the cyotologic and histologic features of a case of pituitary adenoma with immunohistochemical study.