PurposeThe purpose of this chapter is to review hormonal therapy in cryptorchidism in boys to improve fertility.MethodsMultiple searches, primarily in PubMed, were performed using various combinations of the terms: cryptorchidism, undescended testis (UDT), hormonal therapy, fertility, infertility, germ cell numbers, spermatogonia and semen analyses. In additions the pertinent articles from the reference lists in these papers were also obtained and reviewed.ResultsData on fertility in unilateral cryptorchidism does not reveal a significant risk for infertility. Testes biopsies in childhood do not correlate with fertility parameters in adulthood. In bilateral cryptorchidism there is a significant risk of infertility. Results of hormonal treatment were not reported separately for bilateral cryptorchidism. Current data is insufficient to know if hormonal therapy is efficacious in bilateral UDT.ConclusionsHormonal therapy should not be used in childhood to improve fertility in cases of unilateral cryptorchidism. Testes biopsies in childhood to identify those at risk for infertility should not be performed in unilateral cryptorchidism. More data are needed to answer whether hormonal therapy is beneficial in bilateral UDT. There is insufficient data to establish that testis biopsies are helpful in bilateral cryptorchidism in identifying the subgroup with risk for infertility. They should not be performed in the routine clinical setting but may have a role in a research protocol.