A patient on intravenous heparin is described who developed an acute hemorrhagic necrosis of her legs. Thrombi without vasculitis were seen in the dermal blood vessels. This appears to be the 4th reported case of skin necrosis after intravenous heparin at sites unrelated to injections. Skin necrosis after intravenous heparin should warn the dermatologist of a possible fatal outcome from myocardial or cerebral infarction.