Pituitary tumors account 10% of all intracranial neoplasms. The most common pituitory tumor is adenoma arising from anterior lobe. Microadenoma of they are less than 1 cm in diameter. Macroadenoma if they are more than 1 cm in diameter. Most tumors are microadenoma. Microadenomas are the most common cause of hypetpituitrism. Most common pituitary microadenoma is prolactinoma. GH-secreting adenoma is the second most common. As the adenomas expand, they frequently erod the sella turcica and anterior clinoid process. They may compress optic chiasma and cranial nerves. Histologically they can be differentiated by normal pituitary by : -Cellular monomorphism → Adenoma contains single type of cells (e.g., Lactotroph or somatotroph). Absence of reticulin network → Reticulin stain negative, while normal pituitary parenchyma is positive.Corticotroph cell adenomas are PAS postive because of the presence of Carbohydrate in pre-opiomelanocorticotropin (POMC). Hormone negative adenomas are called "null cell adenoma".The majority of pituitary adenomas are sporadic in nature, and only 5%of cases arise as a result on an inherited predisposition. Four genes have been identified this far as a cause of familial pituitary adenoma : MENI, CDDIB, PRKARIA and AIP