Normally the testicles, which form inside the abdomen of a male fetus, descend into the sac beneath the penis (scrotum) by the time the baby is born.

An undescended testicle (cryptorchidism) is one that remains inside the body and has not moved down into the scrotum. One or both testicles may be affected.

Undescended testicles are often classified according to their location and whether they can be felt (palpable or non-palpable).

• Abdominal: The testicle remains inside the abdomen and cannot be felt (is non-palpable) during a physical examination. It is usually near the inner opening of the inguinal canal.
• Inguinal: The testicle stops in the inguinal canal and usually cannot be felt during a physical examination.
• Pre-scrotal or pre-pubic: The testicle moves farther down the inguinal canal but does not descend all the way into the scrotum. It usually can be felt (is palpable) during a physical examination.