The frequency of documented endocrine diseases in rodents and other small mammals varies considerably among the species maintained as pets, biomedical research animals, or display animals in zoos. The clinical diagnosis of endocrine diseases almost never occurs in free-ranging animals in their native habitat. Feral animals that have clinical endocrine disease, such as neoplasia, adrenal cortical hyperplasia, or diabetes, would exhibit clinical signs of altered behavior that would result in their removal by predators. The diagnosis of endocrine disease thus takes place in the relatively protective environment of captivity. This observation should forewarn pet owners and clinicians caring for these animals that the environment contributes to the development of endocrine diseases in these animals.