Heparin-induced thrombocytopenia (HIT) is an idiosyncratic drug reaction first reported in the literature in the 1940's. Two different types of HIT have been identified. Type I, also known as benign, early-onset thrombocytopenia, occurs in as many as 20% of patients receiving heparin and is characterized by up to a 30% reduction in baseline platelet counts during the first few days of therapy. Despite reductions in platelet count, most patients with this type of HIT have platelet values above 100 × 109 cells/L, and this condition usually resolves in a few days without further adverse sequelae.