Natural history of the maldescended testis.

In a series of 545 boys with undescended testis, 91 had bilateral spontaneous descent after the age of 10. Forty-five accepted to take part in an investigation of their fertility based on history, clinical examination, sperm analysis and estimation of serum FSH levels. In the majority, the volume of the testis was below normal and the sperm concentration was below the lower limit of the normal range. It is concluded that late spontaneous bilateral descent of the testis carries a serious risk of later impaired spermatogenesis.