An undescended testis (see TESTICLE). The testes normally descend into the scrotum during the seventh month of gestation; until then, the testis is an abdominal organ. If the testes do not descend before the first year of life, they usually remain undescended until puberty – and even then, descent is not achieved in some instances. Fertility is impaired when one testis is affected and is usually absent in the bilateral cases. The incidence of undescended testis in full-term children at birth is 6 per cent, falling to less than 2 per cent at one month and 0·7 per cent at one year. Because of the threefold greater risk of developing testicular cancer, undescended testes should be brought down as early as possible and at the latest by the age of two. Sometimes medical treatment with HUMAN CHORIONIC GONADOTROPHIN is helpful but frequently surgical interference is necessary. This is the operation of orchidopexy.