Defensive medicine includes medical practices that exonerate physicians from liability without benefit to patients. The national prevalence of defensive medicine in orthopaedic trauma surgery has not been investigated. In September 2010, 2000 orthopaedic surgeons randomly chosen from the American Academy of Orthopaedic Surgeons registry received invitations to answer a survey on defensive medicine. Among these surgeons, 1214 (61%) completed the survey and 222 (18.5%) identified themselves as nonmilitary orthopaedic traumatologists. Cost analysis was performed using Centers for Medicare and Medicaid data at the 2011 current procedural terminology code level and then aggregated to reflect the 8 domains of care assessed. For orthopaedic traumatologists, on average 22% of all ordered tests were for defensive reasons (radiography, 19%; computed tomographic scanning, 23%; magnetic resonance imaging, 27%; ultrasound, 42%; referrals, 29%; laboratory tests, 23%; and biopsies, 16%). Defensive hospital admissions averaged 9% each month. Orthopaedic traumatologists reported fewer referrals to specialists compared with non-trauma orthopaedists (P = 0.02), with no significant difference in overall monthly defensive expenditures.Using 2011 current procedural terminology code reimbursement data, defensive medicine costs per respondent were calculated to be approximately $7800 monthly or $94,000/y, which is 20% of each physician's spending. Given the approximately 2724 orthopaedic trauma surgeons in practice in the United States according to the 2010 American Academy of Orthopaedic Surgeons Census, the national cost of defensive medicine for orthopaedic trauma surgery is estimated to be $256.3 million annually. Defensive medicine among orthopaedic trauma surgeons is a significant factor in health care costs and of marginal benefit to patients. Policies aimed at managing liability risk may be useful in containing such practices.