While the testicles are not yet in the scrotum in the fetus, they begin to develop in the abdomen near the kidneys. Later, they migrate downwards close to birth, pass through the inguinal canal and take their place in the scrotum on both sides. In some babies, it is noticed that one of the testicles and rarely both of them are not in the scrotum. The testis remained somewhere on the descent path (mostly in the inguinal canal). It is necessary for the testicles to be at a temperature 1-2°C lower than the normal body temperature in terms of sperm production functions. Normal testicles keep this constant by rising and falling according to the outside temperature. However, it is thought that the testes, which remained high and could not go down at all, were affected by the high temperature and their functions were impaired. People with bilateral undescended testicles have a decreased chance of having children. Since it has been shown that undescended testicles begin to deteriorate from the age of 1, it is advised to wait until the age of 6-12 months at the latest and to bring down the undescended testicles with treatment. A small percentage of the testicles can descend with hormone treatments. However, researchers, mostly surgeons, who think that vast majority of those who do not descend in this way unnecessarily take sex hormones at a young age (some of them have penile growth and hair growth on the penis), prefer to lower the testis to its normal place between the ages of 6-12 months with direct surgical treatment without applying hormone therapy. Even if the child is older, even if the expectation of function is low, a lowering operation (orchiopexy) should be performed because there is a risk of developing cancer in the undescended testicles in adulthood. Since the diagnosis of cancer in undescended testicles will be difficult, the risk of delay is high. Testicular prosthesis can be placed in order to prevent psychological trauma and to provide a normal cosmetic appearance in some children whose testis had to be removed or who were not developed at all.