Introduction: Clinical decision rules for computed tomography (CT) ordering in pulmonary embolism and mild traumatic brain injury have been shown to be under-used in clinical practice. Current literature does not explain why these validated decision rules continue to be under-used despite evidence of inappropriate use and increased costs. To better evaluate potential barriers to their use, qualitative methods involving focused interviews were conducted amongst emergency department (ED) physicians. Methods: Physicians were recruited via a brief presentation at Calgary Zone ED rounds. Ten attending and resident physicians (4 female, 6 male) were interviewed. Questions were designed to evaluate potential barriers to the integration of decision rules into the computerized order entry system. Interviews were audio-recorded and transcribed manually. A high-level thematic analysis was conducted to draw primary themes from open-ended questions, and responses were totaled for closed-ended questions. Results: Emerging themes suggest concerns surrounding timing of rule application in relation to test ordering, patient influences on ordering, and overuse reporting. All 10 physicians believed decision rules for CT ordering play a large role in the ED, and 8 were in favor of integration into the order entry system. However, over half expressed concern, noting that their thought process begins before order entry. A majority prioritized shared decision-making with patients. However, 8 indicated that patient expectations influence their ordering. A majority agreed that there is CT overuse in the ED, but many were hesitant in concluding that overuse was primarily physician dependent. Conclusion: Primary barriers to decision rule integration are timing of application, hesitation surrounding patient input, and uncertainty over data. Physicians often make decisions prior to order entry. Mobile copies of decision rules should be available to better facilitate compliance. Concerns over patient influence on ordering are common. Patient-friendly materials on clinical decision rules should be available to better facilitate shared decision making while still promoting decision rules. While overuse is agreed upon, many prefer to see and track their own ordering data before supporting a physician-targeted intervention. Data reports to physicians may help affirm physician-associated overuse, and reinforce their role in responsible resource utilization.