The migration of the testes from where they develop inside the abdomen to the scrotum occurs in 97% of boys by the time they are born, but the process may be delayed in premature babies. This is referred to as undescended testicles.
If the testes remain hidden inside the abdomen (cryptorchidism) and do not descend into the scrotum, the scrotum is empty and no testicles can be felt, but in some boys the testes can be found in the groin and manipulated into the scrotum by gentle finger movements. An ultrasound scan is sometimes performed to find the missing testes.
If the testes can be manipulated out of the groin into the scrotum no treatment is usually required, but they must be checked regularly to ensure that they do eventually enter and stay in the scrotum. If the testes do not descend in the first year of life, an operation to place them in the correct position is necessary.
A testicle that remains undescended will eventually fail due to overheating, and if both testes are involved, sterility will result. Long-term problems include an increased risk of inguinal hernia, torsion of the testicle and cancer.