INTRODUCTION: Despite the large contribution of surgical expenses to rising health care costs, many surgeons have little knowledge of their operating room (OR) costs. The goal of OR SCORE (OR Surgical Cost Reduction) is to determine whether providing surgeons with cost feedback reduces OR costs. METHODS: We performed a prospective controlled trial from January to December 2015 at University of California San Francisco (UCSF). Each surgeon in the orthopedic, ear, nose, and throat, and neurosurgery departments received standardized scorecards on a monthly basis in 2015. These scorecards included the median surgical supply cost (all disposable, implantable and nonimplantable, items used in the case, eg, spinal hardware, shunt parts, hemostatic agents, sutures) for each surgery type that the surgeon performed in the prior month, compared with the surgeon's baseline (2012-2014) and all UCSF surgeons performing the same procedure during the baseline. Cardiothoracic, general, vascular, pediatric surgery, obstetrics-gynecology, ophthalmology, and urology surgeons served as controls and did not receive snapshots. All surgical departments (intervention or control) were eligible for a departmental financial incentive if they met a 5% cost reduction goal. RESULTS: We observed a 2% decrease in median case costs in our intervention group ($1398-$1307 per case; n = 11 820 cases), compared with a 10% increase in the control ($712-$765; n = 17 227 cases). This represents a total savings of $1 329 867 in our intervention group. After adjusting for case mix index to reflect case complexity, the difference remained significant: 4% decrease in median case costs in the intervention group, vs 5% increase in the control. Two of 3 intervention departments (ENT and orthopedics) met their target cost reduction goals (with decreases of 8% and 6%, respectively), while only 1 of the 7 control groups met the target. CONCLUSION: Our work suggests that cost feedback scorecards may be sufficient to modify surgeon behavior and reduce OR surgical supply costs.