Coinfection with human immunodeficiency virus (HIV) has a major effect on the natural history of many infectious diseases, particularly mycobacterial diseases. Early in the HIV epidemic, it was predicted that HIV infection would worsen leprosy outcomes, with more patients developing lepromatous disease, an impaired response to multidrug therapy and fewer reactions. However, studies on the epidemiologic and clinical aspects of leprosy suggest that the course of leprosy in coinfected patients has not been greatly altered by HIV. In contrast, initiation of antiretroviral treatment has been reported to be associated with activation of subclinical Mycobacterium leprae infection and exacerbation of existing leprosy lesions. With regular new discoveries about the interaction of leprosy and HIV, the need to maintain research in this field is of considerable importance.