We report of case of one monozygotic twin sister with pituitary tumor and multiple endocrine neoplasia, type 1.The older sister, 31-year-old woman, had undergone Gamma Knife radiosurgery for prolactin producing pituitary microadenoma. Four years later, pancreatic insulinoma was detected, distal pancreatectomy and splenectomy were done. The younger sister, 31-year-old woman, had been operated for pancreatic insulinoma, 12 years ago. One year ago, hyperparathyroidism and pituitary macroadenoma were detected. Tumor removal was followed by Gamma Knife radiosurgery for residual tumor.