One of the most common complications that can occur with the testes is an undescended testis, which typically occurs in about two to four percent of all male infants and around thirty percent of boys born prematurely. This occurs when the testes, which form in the abdomen, fail to descend into the scrotum when puberty begins. This can be addressed by either waiting around three to six months after the initial examination for the testis to descend, or with a surgical procedure called an Orchidopexy, which involves artificially moving the testis to the scrotum. The procedure has a 95 percent success rate.
The relative size of testes is often influenced by mating systems .  Testicular size as a proportion of body weight varies widely. In the mammalian kingdom, there is a tendency for testicular size to correspond with multiple mates (., harems, polygamy ). Production of testicular output sperm and spermatic fluid is also larger in polygamous animals, possibly a spermatogenic competition for survival. The testes of the right whale are likely to be the largest of any animal, each weighing around 500 kg (1,100 lb).