In clinical use for over 50 years, heparin is an important and widely used anticoagulant for the prophylaxis or treatment of thromboembolic disease as well as other numerous clinical situations. Ordinarily, heparin prevents clotting and does not affect the platelets, components of the blood that help to form blood clots. However, heparin can also cause heparin-induced thrombocytopenia. Two distinct types of heparin-induced thrombocytopenia can occur: nonimmune and immune mediated. Nonimmune heparin-induced thrombocytopenia, which occurs most frequently, is characterized by a mild decrease in the platelet count and is not harmful. The second type, immune-mediated heparin-induced thrombocytopenia, occurs much less frequently but is dangerous. Immune-mediated heparin-induced thrombocytopenia causes much lower platelet count. Paradoxically, despite a very low platelet count, patients who suffer from heparin-induced thrombocytopenia are at risk for arterial or venous thrombosis. In this review article, there are discussed about pathogenesis of heparin-induced thrombocytopenia, other causes of thrombocytopenia, clinical features, laboratory confirmation of diagnosis, and management of patients (direct thrombin inhibitors, other therapies, duration of therapy, and use of oral anticoagulants). Prognosis and prophylaxis of this life-threatening disorder, which can develop from the use of unfractionated or (less commonly) low-molecular-weight heparin, are also discussed.