SummaryA patient with heparin induced thrombocytopenia and subsequent disseminated intravascular coagulation and arterial thromboembolism is described. This rare complication of heparin therapy is often difficult to recognize. Pathophysiology is only partially understood. Heparin therapy must be stopped and another form of anticoagulation should be started. Surgery is sometimes necessary to treat the complications. When heparin induced thrombocytopenia is not recognized, it may lead to major complications and sometimes even to death. The diagnosis is confirmed by the demonstration that the serum of the patient causes platelet aggregation in the presence of heparin.