Visceral Leishmaniasis (VL) is a serious protozoal disease endemic in diverse areas, including the southern area of Madrid (Spain), where an outbreak was detected in 2009. The objective of this work is to analyze bone marrow alterations in VL patients and elaborate a diagnostic model with the aim to improve the early detection of this disease. The usual diagnostic methods, as the observation of the parasite on a bone marrow aspirate, have frequent false negatives, and the high sensitivity methods, as PCR and ELISA, are delayed or are not always available.