An undescended testis is when the testis is not fully down in the boy’s scrotum. The testis first develops near the kidney when the baby boy is inside the mother’s womb. For the testis to drop down into the scrotum there needs to be a passage through the groin area. Sometimes the testis remains inside the tummy cavity, but much more commonly it becomes stuck in or close to the groin passage. An undescended testis is not uncommon at birth, especially in premature boys. The testis may ‘drop’ of its own accord in the first 6 months of life, but is very unlikely to do so after this time. The testis needs to be located in the scrotum in order for it to be kept cooler then the rest of the body and to produce normal sperm when the boy is older. Ideally this operation should be performed before the boy is 12 months of age.