Some people with adult growth hormone (hGH or GH) deficiency were not GH-deficient as children. These people are said to have adult-onset GH deficiency.

The most usual cause of adult-onset GH deficiency is damage to the pituitary gland, which is responsible for secreting GH.

Damage is most commonly caused by tumors in and around the pituitary. These tumor may compress the gland, or the damage may occur when the tumor is removed.

The pituitary gland may also be damaged by infection, blood vessel disease, severe head injury, or radiation treatment for tumors of the head or neck.