Background Rising use of computed tomography (CT) to evaluate patients with trauma has increased both patient costs and risk of cancer from ionizing radiation, without demonstrable improvements in outcome. Patient-centred care mandates disclosure of the potential risks, costs and benefits of diagnostic testing whenever possible. Objective We sought to determine (1) patient preferences regarding emergency department (ED) real-time discussions of risks and costs of CT during their trauma evaluations; and (2) whether varying levels of odds of detection of life-threatening injury (LTI) were associated with changes in patient preferences for CT. Methods Excluding patients already receiving CT and patients with altered mental status, we surveyed adult, English-speaking patients at four Level I verified trauma centres. After informing subjects of cancer risks associated with chest CT, we used hypothetical scenarios with varying LTIs to assess patients' preferences regarding CT. Results Of 941 patients enrolled, 50% were male and their mean age was 42 years. Most patients stated they would prefer to discuss CT radiation risks (73.5%, 95% CI [66.1-80.8]) and costs (53.2%, 95% CI [46.1-60.4]) with physicians. As the odds of detecting LTI decreased, preferences for receiving CT decreased accordingly: LTI 25% (desire 91.2%, 95% CI [89.4-93.1]), LTI 10% (desire 79.3%, 95% CI [76.7-81.9]), LTI 5% (desire 69.1%, 95% CI [66.1-72.1]) and LTI <2% (desire 53.8%, 95% CI [50.6-57.0]). If the LTI was <2% and subjects were required to pay $1000 out-of-pocket, only 34.5% (95% CI 31.4-37.5) would opt for CT. Conclusion Most non-critically injured patients prefer to discuss radiation risks and costs of CT prior to receiving imaging. As the odds of detecting LTI decrease, fewer patients prefer to have CT; at an LTI threshold of 2%, approximately half of patients would prefer to forego CT. Adding out-of-pocket costs reduced this proportion to one-third of patients. © 2014 Elsevier Ltd.