Defensive medicine is defined as medical practices that may exonerate physicians from liability without significant benefit to patients. No study has evaluated the United States national incidence of defensive medicine in the field of orthopedic surgery. In the study reported here, we investigated the practice of defensive medicine and the resultant financial implications of such behavior by orthopedic surgeons in the US. A Web-based survey was sent to 2000 orthopedic surgeons in the US. Of the 1214 respondents, 1168 (96%) reported having practiced defensive medicine by ordering imaging, laboratory tests, specialist referrals, or hospital admissions mainly to avoid possible malpractice liability. On average, 24% of all ordered tests were for defensive reasons. Mean national Medicare payment information was used to calculate the cost of defensive medicine per respondent: approximately $100,000 per year. With there being 20,400 practicing orthopedic surgeons in the US, we estimated that the national cost of defensive medicine for the specialty of orthopedic surgery is $2 billion annually. Orthopedic surgeons' defensive medicine is a significant factor in health care costs and is of marginal benefit to patients. Policies aimed at managing liability risk may be useful in containing such practices.