TSH-secreting pituitary adenomas are aggressive, invasive tumors due to their silent features and occasionally may have poor response to available surgical and medical treatments. Inappropriate release of thyrotropin by these tumors can result in hyperthyroidism. The management includes agents that selectively suppress TSH hypersecretion both in patients with TSH-secreting tumor in whom pituitary surgery was unsuccessful and in those with selective pituitary resistance to thyroid hormone action. Among such agents, somatostatin administration has proven to be effective in blocking TSH hypersecretion. We experienced a case of 55-year old female with hyperthyroidism due to TSH- secreting pituitary adenoma. We treated her with the long-acting somatostatin analogue, octreotide, which was administered by subcutaneous injection in doses of 150 ㎍ every 12 hours for first 30 days, and thereafter in doses of 200 ㎍ bid for next 3 months. Serum levels of thyrotropin were dramatically reduced and also tumor size was significantly reduced. We assert that a potent and long-acting analog of somatostatin administration is an effective treatment for patients with neoplastic inappropriate secretion of TSH disorder able to suppress TSH hypersecretion from the adenomatous thyrotrophs and to restore clinical and biochemical euthyroidism in such patients. So we present this case of TSH-secreting pituitary adenoma with a literature review.