The great majority of viral infections are not associated with significant alterations in hemostasis. Occasionally, common viral pathogens lead to illnesses in which hemostatic impairment is an important feature. In these instances, two clinical syndromes usually are present: thrombocytopenic purpura and disseminated intravascular coagulation. Immune mechanisms are implicated in the first, while the second is associated with severe disease. Hepatitis viruses produce hemorrhage by a third mechanism. In cases of fulminant hepatitis, hepatocellular injury leads to decreased production of multiple coagulation factors and impairment of other hepatic functions that modulate hemostasis. A small number of viruses stand apart by virtue of the frequency with which they cause hemorrhage. These are the hemorrhagic fever viruses. Much more needs to be learned about how these viruses cause disease and induce hemorrhage. The first line of therapy in viral infections complicated by hemorrhage is early treatment with an antiviral agent. Unfortunately, effective antiviral therapy is usually not available. There is little useful information and no controlled studies on the efficacy of therapy aimed directly at correcting hemostatic impairment.