The value of nonhuman primates as models for a variety of human diseases is well documented. These species have been used extensively during the past 25 years or so as models for a variety of bacterial, viral, and parasitic diseases, either as naturally occurring or experimentally induced infections. They are often the only nonhuman species susceptible to experimental infection with agents of human disease. Spontaneous diseases of nonhuman primates are often comparable to human diseases, and with the continued long-term maintenance of nonhuman primates in the laboratory as well as in domestic breeding colonies, it is reasonable to assume that additional disease models will be discovered. Such models may include degenerative diseases, diseases and/or lesions associated with the aging process, and genetic diseases. In this article we have reviewed four spontaneous diseases and one induced disease that have essentially identical counterparts in humans. Three of these are bacterial diseases that currently cause severe and sometimes fatal infections in humans; one is a degenerative disease that is usually progressive and fatal in humans, and one is possibly a genetic disease for which there is currently no animal model. The clinical and pathologic similarities between these nonhuman primate diseases and their human counterpart make these nonhuman primate diseases potentially valuable models for further studies on the etiology, pathogenesis, and treatment of these serious and often fatal human diseases.