Background: The standard evaluation of patients with right upper quadrant (RUQ) abdominal pain consists of a history and physical examination, laboratory analysis, and radiological investigation. Given the increasing availability of bedside ultrasound in 'the Emergency Department (ED), a growing proportion of Emergency Physicians are now performing their own ultrasound examinations in patients with RUQ abdominal pain to circumvent diagnostic delays and improve patient care. Objective: To determine the economic "opportunity" costs of additional radiographic testing after identification of acute cholecystitis by focused ED ultrasound performed by registered diagnostic medical sonographer (RDMS)-certified personnel. Methods: A retrospective analysis of a consecutive sample of patients with "positive" focused ED ultrasounds of the RUQ that were significant for cholecystitis, who presented from June 1, 2005 through February 30, 2006. Cost analysis was performed using standard Medicare compensation indices for radiological examinations of the abdomen/hepatobiliary system. Results: There were 37 patients enrolled; 32 patients exhibited RUQ pain with a focused ED ultrasound significant for cholecystitis. Eight (25%) patients received no further radiographic tests and exhibited positive pathology. Twenty-four (75%) patients had additional diagnostic examinations; 22 (92%) showed positive pathology. Based upon Medicare compensation indices, an opportunity cost of $6885.34 was incurred at our institution over 9 months due to additional examinations. Using nationally comparable indices, this was extrapolated to an opportunity cost of $63 million (95% confidence interval $48.3-$78.9 million) per year across the nation, assuming that 50% of patients with cholecystitis present to the ED and receive an ultrasound examination by an RDMS-certified Emergency Physician. Conclusions: In this small sample, additional radiological testing after Ell ultrasounds significant for acute cholecystitis led to sizable economic costs on a local and national level. Formal cost-benefit analyses are needed to evaluate the full economic and patient care implications of ED ultrasound use in this setting. (C) 2010 Elsevier Inc.