We have studied a form of leishmaniasis (Leishmaniasis cutis diffusa) that we consider to be a variety of American cutaneous leishmaniasis with clinical, immunological, parasitological, and evolutive characteristics of its own, which distinguish it from the common American cutaneous type. We believe the causative agent to be a variant of L braziliensis with characteristics specific for its strain. In Venezuela 16 cases of the disease are known to date, and the majority of them have been followed clinically for many years. The disease begins with a localized lesion which may be an ulcer, a nodule, or a plaque. Thereafter follow satellite lesions in the vicinity of the initial manifestation. Lesions appear later at a distance and they tend to become disseminated till they cover practically the whole dermis with the exception of the scalp and the inguinocrural region. The lesions of the nasal mucous membrane are discrete and characterized by a superficial infiltration that never develops into the destructive lesions that are so common in infestions with the current American cutaneous type of Leishmania. Another characteristic of the disease is its slow, persistent progress in spite of treatment with the known leishmanicidal drugs. This resistance to pharmacotherapy is an inalienable trait of the parasite in lesions of long duration, a characteristic that it does not lose when transferred to an animal host. The incipient lesions, nevertheless, do respond well to treatment. This has been proved during several years of observation of such cases.