Cryptorchidism
（重定向自Cryptorchid）
Cryptorchidism is the absence of one or both testes from the scrotum. It is the most common birth defect of the male genitals. About 3% of full-term and 30% of premature infant boys are born with at least one undescended testis. However, about 80% of cryptorchid testes descend by the first year of life (the majority within three months), making the true incidence of cryptorchidism around 1% overall. Cryptorchidism may develop after infancy, sometimes as late as young adulthood, but that is exceptional.