Condition in which the internal sex glands (testicles or ovaries) produce too few hormones and/or sex cells. The cause can lie in the organs themselves, or in the pituitary gland, which is responsible for stimulation of the sex organs. The condition can be congenital, or can arise from later genital disorders such as infection or cysts or tumours of the testicles or ovaries. A special form of the condition occurs if the pituitary gland produces too few stimulating hormones. Hypogonadism usually causes fertility problems because of sperm abnormalities or failure to ovulate. In some cases there may also be abnormalities of the external genital organs. Sex hormone therapy can only be effective if the ovaries and testicles are themselves intact.