Many forms of stress, including psychological, can affect male fertility and reproduction. The autonomic nervous system and the adrenal hormones participate in the classic stress response while also affecting the reproductive system. Evidence exists that mild-to-severe emotional stress depresses testosterone and perhaps interferes with spermatogenesis in the human male. There are difficulties, however, in attributing individual cases of infertility to psychological factors without evidence of psychopathology. In animals social stress, high altitude, surgery, and immobilization stress affect body weight, testosterone levels, and copulatory behavior with variable effects on testicular morphology. Stress applied to the pregnant rat also affects the development and sexual behavior of the male offspring. This literature is reviewed and discussed in terms of the usefulness of animal models and suggested future research.