Normally testicles develop in the abdomen, near the kidney, and descend through the abdominal wall, then through the inguinal canal, and enter the scrotum. Cryptorchidism (or undescended testes) is a condition seen in newborns when one or both of the male testes have not passed down into the scrotal sac. Thirty percent of cases are bilateral (involve both testes).
Undescended testes may occur for several reasons. Known causes may include hormonal disorders, abdominal wall disorders, and chromosomal defects. Retractile testes can occur in boys where the testicle descended completely but a muscle reflex causes a testicle to move back and forth from the scrotum to the groin.