Multiple endocrine neoplasia type 1 (MEN 1) is the association of neoplastic transformation of parathyroid, pituitary, and pancreatic islet cells. This syndrome is inherited as an autosomal dominant trait. A 38-year-old woman presented with general weakness and mental changes. She had experienced same symptoms 7 years ago, after then her weight gradually increased. Insulinoma was suspected by markedly decreased blood glucose level (20mg/dL) and the increased insulin/glucose ratio (0.43) that sampled in emergency room at the time of mental change. Unusually large pancreatic tail mass and Lt, adrenal gland mass were detected by abdominal CT. Percutaneous transhepatic portal vein catheterization with insulin sampling showed sudden step up of insulin/glucose ratio at the middle portion of pancreas. Measuring of basal pituitary hormones as a screening procedure of MEN showed increased basal prolactin level. Combined pituitary stimulation test showed blunted response of prolactin to TRH and sellar magnetic resonance imaging showed intrasellar mass. Thyroid nodule was palpated on her anterior neck. Thyroid scintigram showed cold nodule, and there was no lymphadenopathy around the nodule by the thyroid sonogram. Fine needle aspiration cytology showed benign hyperplastic follicular cells only. Serum ionized calcium and parathyroid hormone level were normal. Under the impression of MEN type I, the distal pancreatectomy, splenectomy, Lt. thyroid lobectomy and Lt. adrenalectomy was performed at the same time. Histologic examination of the surgically removed tissues revealed pancreas islet cell tumor, adrenal cortical adenoma and thyroid adenoma. Transient hyperglycemia was developed after surgical intervention, but thereafter she never felt any symptoms of hypoglycemia till now and her blood glucose showed completely normal level with oral glucose tolerance tests. We present this case with a review of literature.