When do boys have their testicles drop?

In 9th month usually: Generally they descend into the scrotal sac during the 9th month of pregnancy, sometimes earlier. Some boys are born with undescended testicle(s). If there are no other associated medical issues, they usually come down by 6 months of age. Very few are still undescended by that time. These need to be followed closely and will likely need to be brought down surgically as it may affect fertility.