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Objectives: To evaluate the hypothesis that computed tomography (CT) angiography often yields a result interpreted as an alternative diagnosis to pulmonary embolism (PE) in emergency department (ED) patients., Methods: This was a multicenter, retrospective, and secondary analysis of consecutive patients in three academic emergency departments. ED patients with symptoms suspicious for PE were included. CT angiography was ordered at the discretion of the treating physician; patients were identified by query of the electronic medical record. Board-certified radiologists gave CT readings, which were reviewed by two independent emergency physicians who categorized the non-PE findings into one of four acuity categories: A = requiring specific and immediate intervention, B = requiring specific action on follow-up, C = requiring no action, and D = indeterminate findings., Results: The prevalence of PE among the 1,025 patients studied was 10% (95% CI = 8% to 12%). In the 921 patients without PE, the mean prevalences (ranges between sites) of concordant categorized non-PE findings were: A = 7% (range 3%-11%), B = 10% (7%-13%), C = 17% (10%-20%), D = 4% (0%-8%), and no ancillary finding = 41% (29% to 45%). The most common category A findings included infiltrate or consolidation suggesting pneumonia (81%), aortic aneurysm or dissection (7%), and mass suggesting undiagnosed malignancy (7%). The overall unweighted agreement was 80% (kappa = 0.72) and weighted agreement was 93% (kappa(w) = 0.84)., Conclusions: In ED patients with suspected PE, the CT angiogram frequently provides evidence suggesting an important alternative diagnosis to PE. Pulmonary infiltrate suggesting pneumonia was the most common non-PE finding.