Thyrotroph cell adenoma is a rare disorder characterized by high T4 and T3 as well as elevated serum TSH level. A 41 year old women with a hyperthyroidism was found to have pituitary tumor with a elevated serum TSH level. Transsphenoidal microsurgery and radiotherapy normalized the serum TSH and thyroid hormone level. Immunostaining with antiserum to human TSH and electron microscopy of the tumor confirmed confirmed thyrotroph cell adenoma. We present this case of thyrotroph cell adenoma with a literature review. (J Kor Soc Endocrinol 5:302 307, 1990).