Visceral leishmaniasis is a serious infectious disease caused by an obligate intracellular protozoan of the genus Leishmania. The disease encompasses a wide spectrum of clinical manifestations, which can range from asymptomatic cases, to the classical form of the disease characterized by hepatosplenomegaly, fever and wasting, and even the more severe bleeding that can progress to death. Some factors can alter the severity of clinical manifestations, among them the genetic predisposition. Through research of genetic polymorphism it is possible to evaluate which genes may be related to susceptibility to infection and predisposition to the most severe forms of the disease