Hematologic factors, in particular platelets and the coagulation system, play an important role in the pathogenesis of organ failure in the intensive care unit. Failure of these hematologic systems is common in intensive care patients and may range from isolated thrombocytopenia or prolonged global clotting tests to complex defects, such as disseminated intravascular coagulation. There are many causes for a deranged coagulation in critically ill patients, and each of these underlying disorders may require specific therapeutic management. Hence, a proper differential diagnosis and initiation of adequate (supportive) treatment strategies are crucial to reduce morbidity and mortality in critically ill patients with coagulation abnormalities.