The different species of Leishmania are continuously in a state of flux due to the lack of easy means of differentiating species. Basically, there are three major groups of organisms: those which cause visceral disease, those which cause cutaneous lesions, and those which cause mucocutaneous lesions. The organisms causing visceral disease are species and various subspecies of Leishmania donovani. The organisms causing cutaneous leishmaniases in the Old World are Leishmania tropica (anthroponotic or urban cutaneous leishmaniasis with dry lesions), Leishmania major (zoonotic or rural cutaneous leishmaniasis with wet lesions), and Leishmania aethiopica (zoonotic cutaneous leishmaniasis of Kenya and Ethiopia with varied lesions). The organisms causing zoonotic cutaneous leishmani ases in the New World are Leishmania braziliensis, Leishmania mexicana, and Leishmania peruviana. The organisms causing mucocutaneous leishmaniases in the New World are typically due to species of Leishmania braziliensis.