OBJECTIVE To describe a case of a thyrotropin-secreting pituitary adenoma that responded to bromocriptine therapy by suppression of thyrotropin and tumor shrinkage. METHODS We present the clinical course, laboratory data, and radiographic findings in a 32-year-old woman with a thyrotropin-secreting pituitary adenoma before and after treatment with bromocriptine. RESULTS The patient's pituitary tumor was detected after she had been treated with radioactive iodine for thyrotoxicosis presumed to be due to Graves' disease. After thyroid ablation, the thyrotropin levels could not be brought into the normal range, even while the patient was receiving supraphysiologic doses of orally administered levothyroxine. Magnetic resonance imaging of the pituitary, along with hormonal workup, confirmed the diagnosis of a thyrotropin-secreting pituitary adenoma. Because the tumor was not threatening vital structures and was considered incurable by operation, medical therapy was elected. A trial of bromocriptine was initiated at 15 mg/day and increased to 30 mg/day in three divided doses. Follow-up hormonal studies showed that thyrotropin levels declined into the suppressed range, and repeated magnetic resonance imaging scans showed substantial shrinkage of the pituitary lesion. CONCLUSIONS Thyrotropin-secreting tumors may respond hormonally and structurally to bromocriptine therapy. In patients with such tumors, a trial of dopamine agonists at high dose may be considered before initiation of more invasive medical treatment.