Undescended testicle occurs when one or both testicles fail to move into the scrotum before birth.

Undescended testicles are fairly common in premature infants. They occur in about 3 - 4% of full-term infants. In most cases the testicles descend by the time the child is 9 months old.

Once a testicle has been discovered in the scrotum, it is generally considered descended even if it is temporarily pulled back (retracted) on a later examination.

Sometimes a condition called retractile testes will develop. In this condition, the health care provider can sometimes locate the testicles and sometimes not.

This occurs because of the strength of the muscle reflex (cremasteric reflex) that retracts the testicles and the small size of the testicles before puberty. In this instance, the testicles descend at puberty. This is considered a type of normal. Surgical correction is not needed.

Testicles that do not descend by the time the child is 1 year old should be carefully evaluated. Studies suggest that surgery should be done by this age to confirm the diagnosis and to reduce the chances of permanent damage to the testicles.

Testicles that do not naturally descend into the scrotum are considered abnormal. These undescended testicles have an increased likelihood of developing cancer, regardless of whether or not they are brought down into the scrotum.

Bringing the testicle into the scrotum maximizes sperm production and increases the odds of good fertility. It also allows examination for early detection of testicular cancer.

In other cases, such as vanished testis, no testicle may be found, even during a surgical procedure. This may be due to a problem that occurs while the baby was still developing in the mother. It may be present at birth (congenital).