Context: Emergency Physician ultrasound has recently emerged as a potential method for the clinical identification of acute cholecystitis. Objective: To determine the accuracy and cost-savings of Emergency Physician ultrasound performed by RDMS certified personnel in the detection of acute cholecystitis. Design, Setting, and Participants: Retrospective analysis of quality assurance data from 37 patients that presented to the emergency department (ED) of an academic, tertiary care hospital with ‘positive’ ED ultrasounds of the RUQ from June 1, 2005 to February 30, 2006. Main Outcome Measure: Positive predictive value (PPV) for ED ultrasound to detect acute cholecystitis with subsequently confirmed surgical pathology. Secondary outcomes were the hypothetical cost-savings achieved with singular use of ED ultrasound, without additional radiographic modalities, to identify and diagnose cholecystitis as extrapolated to the hospital, state, and national level. Results: Thirty-seven patients were studied. Five patients were excluded due to prior diagnosis of cholecystitis, flight, or inoperative status. Thirty-two patients, 15 males (47%) and 17 females (53%), exhibited new-onset RUQ pain with an ED ultrasound significant for cholecystitis. Eight (25%) patients received no further radiographic tests and all exhibited positive surgical pathology. Twenty-six (75%) patients had additional scans (radiology-performed ultrasound, DISIDA scan, both), of which 24 (92%) showed positive surgical pathology. The PPV for ED ultrasound to detect acute cholecystitis with surgical pathology was 94%. Based upon Medicare compensation indices, an opportunity cost of $6885.34 was incurred at our institution over 6 months as a result of additional scans. Using conservative estimates of the prevalence of gallstones and US population distribution, this can be extrapolated to a $83 million potential cost-saving at the national level. Conclusions: ED ultrasounds performed by RDMS certified physicians are accurate and cost-efficient at identifying acute cholecystitis. Larger, prospective studies are needed to more accurately determine the health-care costs associated with this phenomenon.