Underfunction of the testes leads to testosterone deficiency. The medical term for this is hypogonadism.

A shortage of testosterone can cause a wide range of symptoms and serious diseases in men.

Testosterone deficiency can have many causes. It can be present at birth or can develop later in life (e.g. as a result of illness or injury).

It has been recognized that a testosterone deficiency is also common in the aging male. About one third of all men in the second half of life are affected.

The symptoms and consequences of a testosterone deficiency depend on whether the hormone deficiency occurs before birth, before puberty or only after reaching adulthood.