Abstract
A 23 yr old man with secondary hypogonadism was also thyrotoxic. Results of thyroid function tests were in the hyperthyroid range but the serum TSH [thyroid stimulating hormone] was inappropriately high. A pituitary tumor was demonstrated and following hypophysectomy he became biochemically hypothyroid. Evidence is presented and discussed that his hyperthyroidism was due to excessive TSH production by the pituitary tumor.