Cryptorchidism is the most common disorder of sexual differentiation in males, with an incidence of 3.4 per cent in the term newborn, decreasing to 0.8 per cent at 1 year of age. The mechanisms of normal testicular descent are multifactorial and include an intact hypothalamic-pituitary-testicular axis, as well as a normal gubernaculum and epididymis. In boys with cryptorchidism, the testes demonstrate degenerative changes histologically as early as 1 to 2 years of age. Both testes may be affected, even with a unilateral undescended testis. The most important long-term complications of cryptorchidism include infertility and testicular cancer. The risk of malignancy is 10 to 40 times higher in men with cryptorchidism than in normal men and is highest in men who have had an intra-abdominal testis and in certain intersex conditions. Orchiopexy does not appear to lessen this risk. In clinical trials in the United States, hormonal therapy with hCG or GnRH has not been effective in causing testicular descent; therefore, orchiopexy remains standard treatment. However, hCG is recommended if the clinician suspects that a testis is retractile. Orchiopexy should be performed between 12 and 18 months of age to prevent the degenerative changes that are demonstrable by 2 years.