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BACKGROUND: Ultrasound (US) is the preferred initial diagnostic image test for evaluating patients with suspected gallstone disease. Compared to US, computed tomography scans (CT) are more expensive, associated with significant radiation exposure, and have lower sensitivity, positive and negative predictive value for gallstone disease.METHODS: This is a retrospective review of a prospectively collected database of patients emergently admitted with acute biliary disease to our institution between January 2005 and May 2010. The use of CT and US imaging on admission was described, and multivariate logistic regression was used to evaluate factors predicting receipt of CT.RESULTS: From January 2005 to May 2010, 562 consecutive patients presented to the emergency department with complicated gallstone disease. Patients had a mean age of 45+20 years. Seventy percent of patients were female, 46% were white, and 41% were Hispanic. Sixty-five percent of patients had acute cholecystitis, 24% had gallstone pancreatitis, and 11% had common bile duct stones as the admitting diagnosis. A total of 493 patients underwent imaging during admission. Overall, 42% of patients (n = 234) underwent CT. Approximately 25% of patients (n = 141) underwent both CT and US, while 47% (n = 259) and 16% (n = 93) respectively underwent US or CT only. In those who underwent both imaging procedures, CT was performed prior to ultrasound in 67% of patients. Patients undergoing imaging in the evening (7pm - 7am) were nearly four times more likely to get a CT (OR 3.87, 95% CI 2.63-5.69). In addition, increasing age (by 5 years increments, OR 1.14, 95% CI 1.09-1.21) was associated with increased odds of receiving CT on admission. Weekend admission, gender, race, previous ER visits, and diagnosis (acute cholecystitis vs. gallstone pancreatitis vs. common bile duct stones) did not predict use of CT scanning.CONCLUSIONS: Though US is the initial diagnostic image test and CT is of little additional benefit, our study demonstrates the overuse of CT has in the evaluation of acute, complicated gallstone disease. A large proportion of our sample (41%) underwent CT either alone or in conjunction with US and evening imaging was the biggest predictor of CT use. CT was frequently obtained overnight when US was not available. The results of our multivariate analysis suggest that CT is performed not to clarify the diagnosis, but rather a surrogate for the ideal study. In patients with strong clinical suspicion of complicated gallstone disease, US should be encourage as the initial and only test for evaluation if no other complications are suspected. In case of limited resources, surgeons and emergency physicians should be able to perform good quality bedside right upper quadrant ultrasounds to avoid receipt of unnecessary additional studies.