Will an 18 y.o. with undescended testes be sterile?

No: It depends on the presence and adequate function of the other testicle. An undescended testicle in the abdomen has a low likelihood of producing sperm but one in the groin may produce enough sperm. A testicle that was undescended but was brought down early in life should have enough sperm production for fertility on its own.

Depends: Will be sterile if both testes are undescended and located above the scrotum. Not sterile if one testis is down in the scrotum, however fertility may be impaired and is an other good reason to have the problem corrected as a baby, or as soon as it is recognized after babyhood. A single undescended test can influence the sperm production in the contralateral testis.

Possibly: Sperm will have to be evaluated after testes are surgically corrected. They will check for number, motility, and other characteristics.