Cryptochidism, or undescended testes, is a condition in which a newborn male's testes (one or both) have not descended into the scrotal sac.  It is most commonly found in premature infants, since the descent normally doesn't happen until the seventh month of fetal development.  Causes other than prematurity may include hormonal disorders, spina bifida, retractile testes or testicular absence. 

Your pediatrician will probably discover this condition when he or she is first examining your baby after birth.  Undescended testes often resolves itself by six months.  If the testes do not descend on their own, your son may require surgery at 18 months to fix the condition.  98 percent of the babies who undergo this surgery have the problem completely resolved.  Other treatment may be used such as hormone therapy to stimulate testosterone production, helping the testes to descend into the scrotal sac.