Objective and importance: Thyrotroph cell adenoma accounts for only 1% of all pituitary adenomas. This tumor is tough and firm because of significant interstitial fibrosis, and is difficult to remove. Atypical adenoma has an aggressive biological character, invades the surrounding structures, and grows rapidly. Atypical thyrotroph cell adenoma is extremely rare. Clinical presentation: A 32-year-old man presented with hyperthyroidism and bitemporal hemianopsia. Head magnetic resonance imaging revealed a large sellar tumor compressing the optic chiasma and invading the left cavernous sinus. Intervention: Transsphenoidal surgery was performed and subtotal removal was achieved. Histological examination showed atypical thyrotroph cell adenoma. Gamma knife surgery was planned, but the tumor re-grew within 3 months, and reattached to the optic chiasma. Second transcranial surgery failed to remove residual tumor behind the pituitary stalk. Conventional irradiation followed by octreotide administration resulted in decreased tumor size and stable euthyroidism. The tumor has been controlled for 22 months since first surgery and diagnosis. Conclusion: A typical thyrotroph cell adenoma has an aggressive biological character and grows rapidly. Multimodal treatment including medication and radiotherapy is required.