Normally, they descend into the scrotum before birth.
Undescended testicle occurs when the testicle fails to move into the scrotum prior to birth.
In these cases, the testicles typically descend by 3 months of age. Once a testicle has been discovered in the scrotum, it is generally considered descended even if it is temporarily retracted on a later examination. In this instance, the testicles descend at puberty. Testicles that do not descend by one year of age should be carefully evaluated. Abdominal ultrasound may help determine the presence of testicular material.