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The leishmaniases are a group of zoonotic infections caused by protozoan parasites of the genus Leishmania. These infections produce a variety of different clinical diseases depending on the virulence or tropism of the parasite and differential host immune responses. Newly recognized clinical presentations, such as viscerotropic leishmaniasis in American military veterans of Operation Desert Storm, continue to challenge clinicians. Epidemics of classic visceral leishmaniasis leading to thousands of deaths are ongoing in Brazil, India, and the Sudan. Epidemics of localized cutaneous leishmaniasis are ongoing in many areas of South America, North Africa, and Central Asia. A marked increase in cases is often associated with an influx of nonimmune populations into newly cleared agricultural areas or population expansion into previously unsettled areas surrounding cities. The emergence of leishmaniasis as an important opportunistic infection in AIDS patients portends an ominous future as the HIV pandemic sweeps into the hyperendemic areas of South America, Africa, and the Indian subcontinent. Parenteral transmission via needle sharing in HIV coinfected individuals in Spain is an epidemiologically significant new mode of transmission. Finally, recent work has elucidated an enzootic transmission cycle involving L. mexicana in Texas.