Most of the time, children's testicles descend by the time they are 9 months old. Undescended testicles are fairly common in infants who are born early (premature infants). It occurs in about 3 - 4% of full-term infants.
Once a testicle has been found in the scrotum, it is considered descended, even if it is temporarily pulled back (retracted) during a later examination.
Some babies have a condition called retractile testes, in which the health care provider sometimes cannot find the testicles. This is due to the muscle reflex that retracts the testicles and the small testicle size before puberty. The testicles will descend at puberty. Surgery is not needed.
Testicles that do not descend by the time the child is 1 year old should be evaluated. Studies suggest that surgery should be done by this age. Surgery can reduce the chances of permanent damage to the testicles, which can lead to fertility problems later in life.
Testicles that do not naturally descend into the scrotum are considered abnormal. An undescended testicle is more likely to develop cancer, even if it is brought down into the scrotum. The other testicle is also more likely to develop cancer, even if it descended properly.
Bringing the testicle into the scrotum can improve sperm production and increases the odds of good fertility. It also allows the health care provider to examine the testicle to detect cancer early.
In other cases, no testicle may be found, even during surgery. This may be due to a problem that occurred while the baby was still developing in the mother (congenital).