Abnormalities of testicular descent represent the most common genitourinary anomaly in men. Many aspects of testicular maldescent remain controversial. The etiology of the undescended testis is still not known, but results of experimental work in rats strongly support the hormonal theories. Distinction between the truly undescended testis and the retractile testis remains a problem, making retrospective analysis of previous data confusing. Newer aspects of diagnosis of nonpalpable testes include the human chorionic gonadotropin test, herniography, venography and arteriography. Routine aspects of surgical therapy have changed little in recent years, although newer techniques, such as microsurgical procedures and innovative scrotal anchoring methods, are now available. Malignant tumors and infertility are the most worrisome complications. Evidence is presented to suggest that prognosis is related not only to choice of therapy but also to its timing. The recent evidence for Sertoli cell dysfunction, if substantiated may resolve some of the controversies.