Large pituitary adenomas causing Cushings disease are uncommon, and usually present with mild manifestations of Cushings syndrome. Large adenomas may have rapid growth and quickly reach a size large enough to become clinically apparent. These tumors are more frequently invasive than microadenomas, their widespread extensions make radical surgical removal difficult and the ultimate clinical course malignant. We report a case of 37 year-old women presenting amenorrhea, weight gain, and moon face. Sellar magnetic resonance imaging(MRI) demonstrated a large lobulating tumor measuring 3.5cm in diameter, arising from sella turcica, extending up to suprasellar area and invading the cavernous sinuses. Transfrontal adenectomy was performed to remove a mass, but residual mass was remained after surgery. Subsequent external brain radiotherapy(total dose 5400cGy) was performed. Histology revealed an adrenocorticotrophin(ACTH) secreting pituitary adenoma. After treatment, her menstration was started, body weight was reduced, and moon face was disappeared.