Coccidioidomycosis is a fungal infection, almost always acquired from the environment, that can affect many species of mammals and some reptiles. The fungus is endemic in the soil of the southwestern United States, Mexico, and parts of Central and South America. Its distribution is patchy, but in some “hot spots,” up to 70% of the human population has been infected. Most infections in people are relatively mild or asymptomatic, but severe or fatal illness also occurs, especially in the elderly or immunocompromised. Among animals, coccidioidomycosis is common in dogs, which have a spectrum of illness similar to humans. Cases have also been reported in llamas, nonhuman primates, cats, horses, a wide variety of other domesticated or wild mammals, and a few reptiles such as snakes.