Abstract: Viral hemorrhagic fevers (HF) are a group of acute febrile diseases with high mortality rates. While hemostatic dysfunction appears to be a major determinant of the severity of the disease, it is still unclear what pathogenic mechanisms lead to it. In clinical studies, arenaviruses such as Lassa, Machupo and Guanarito viruses caused HF that vary in symptoms and biological alterations. In this study we aimed to characterize the hemostatic dysfunction induced by arenaviral HF to determine its implication in the severity of the disease and to elucidate the origin of this syndrome. We found that lethal infection with Machupo, Guanarito and Lassa viruses is associated with cutaneo-mucosal, cerebral, digestive and pulmonary hemorrhages. The affected animals developed a severe alteration of the coagulation system, which was concomitant with acute hepatitis, minor deficit of hepatic factor synthesis, presence of a plasmatic inhibitor of coagulation and dysfunction of the fibrinolytic system. Despite signs of increased vascular permeability, endothelial cell infection was not a determinant factor of the hemorrhagic syndrome. There were also alterations of the primary hemostasis during lethal infection, with moderate to severe thrombocytopenia and platelet dysfunction. Finally, we show that lethal infection is accompanied by a reduced hematopoietic potential of the bone marrow. This study provides an unprecedented characterization of the hemostasis defects induced by several highly pathogenic Arenaviruses. Transcriptomics data presented in Figure 3 and in Supp Figure 2