Many key health reform bills in the 103rd Congress include proposals to overhaul the medical malpractice system. One of the factors motivating such legislation is the practice of defensive medicine, or care that does not benefit the patient and is provided solely to avoid malpractice claims. Estimating the costs of defensive medicine is difficult because of the many conflicting and overlapping motivations facing physicians. Although our estimates delineate a wide range of potential savings, systemwide savings from aggressive malpractice reform could approach $41 billion over five years.