Hyperpituitarism is defined to mean too much of one, or perhaps two, of the hormones from the adenohypophysis. This may be due either to autonomous over-production (i.e., from a primary adenoma in this gland [microadenoma, macroadenoma] - cancer of the adenohypophysis is very rare Cancer 79: 804, 1997, J. Neurosurg. 96: 352, 2002), from excess production of hypophyseal stimulating factors or underproduction of inhibiting factors, or loss of inhibition following the destruction of other endocrine glands. Pituitary disease, like other endocrine disease, is fairly common, and is generally treatable if it is discovered. The anterior pituitary (adenohypophysis), produces ACTH, TSH, FSH, LH, GH, and prolactin. If the input from the hypothalamus is interrupted, the adenohypophysis makes more prolactin and less of the other hormones.

The presenting clinical symptoms are due exclusively to overproduction of those hormones normally secreted. The characteristic syndromes are related to the type of hormone secreted. Prolactinomas produce amenorrhoea / galactorrhoea in women and impotence / gynecomastia in men; ACTH secreting tumors produce Cushing's syndrome; growth hormone secreting tumors produce gigantism in children and acromegaly in adults.

Diagnosis is usually made by MRI since the CAT scans are of poorer resolution. Most patients will be treated with drugs, surgery or radiation.