Leishmaniasis is a clinically heterogeneous syndrome caused by intracellular protozoan parasites of the genus Leishmania. The clinical spectrum of leishmaniasis encompasses subclinical (not apparent), localized (skin lesion), and disseminated (cutaneous, mucocutaneous, and visceral) infection. This spectrum of manifestations depends on the immune status of the host, on the parasite, and on immunoinflammatory responses. Visceral leishmaniasis causes high morbidity and mortality in the developing world. Reliable laboratory methods become mandatory for accurate diagnosis, especially in immunocompromised patients such as those infected with HIV. In this article, we review the current state of the diagnostic tools for leishmaniasis, especially the serological test.