Gigantism is an excessive secretion of growth hormone during childhood before the closure of the bone growth plates, which causes overgrowth of the long bones and very tall stature. he vertical growth in height that marks this condition is also accompanied by growth in muscles and organs, which makes the child extremely large for his or her age. The disorder can also delay puberty.

The cause of excess growth hormone secretion is most often a pituitary gland tumor. Giantism may also be caused by an underlying medical condition such as multiple endocrine neoplasia (MEN) type-1, McCune-Albright syndrome (MAS), neurofibromatosis or Carney complex. Pituitary tumors are never malignant (cancerous). If excessive secretion of growth hormone occurs after normal bone growth has stopped, the condition is known as acromegaly.