Current knowledge concerning both morphological and functional cryptorchid-related alterations in the various testicular compartments is summarized in this valuable new publication. Damage to the germinal epithelium and resulting infertility in both humans and experimental animals as well as the degree of damage to the different stages of germ cell development is discussed. In addition, information concerning hormonal therapy and orchidopexy to reverse cryptorchid-related damage is provided. Morphological alterations in Sertoli and Leydig cells is discussed in terms of cellular hypertrophy and hyperplasia, alterations in organelle number and characteristics as well as changes in cell-cell junctional complexes. Changes in Sertoli cell and Leydig cell function, including gonadotropin binding, steroidogenesis and other metabolic alterations is also outlined,as well as the influence of altered testicular function on subsequent hypothalamic-pituitary changes. Vascular disruption, the potential role of paracrine substances and direct thermal damage, all of which may be responsible for the resulting detrimental changes in one or more testicular compartments, are considered.