ABSTRACT The number of computed tomography (CT) examinations performed in urgent care has been increasing since its introduction in the emergency room (ER). This has led to a substantial increase in hospital costs and patient’s exposure to ionizing radiation, which has led to the need for more judicious use of CT in the ER. The aim of this study is to show the difference between clinical (pre-CT), tomographic (post-CT) and definitive diagnoses in patients with abdominal CT in the ER. This is a cross-sectional study, with retrospective data collection through electronic medical records. A total of 834 patients with acute abdominal pain (AAP) lasting less than 7 days, submitted to abdominal computed tomography between January 1, 2016 and December 31, 2017 were selected. Clinical, tomographic and final diagnoses were recorded and submitted to a concordance analysis by calculating the Kappa coefficient, considering p <0.05 as significant. CT scans were considered unnecessary when the clinical diagnosis was concordant when both final and post-CT diagnosis were also concordant. The most frequent diagnoses were nonspecific abdominal pain (NSAP), obstructive uropathy (OU) and appendicitis (AP), corresponding to 73.6%, 58.5% and 61.3% of all diagnoses, respectively. Data analysis showed a moderate Concordance for NSAP (kappa: 0.41, p ¬<0.001) and for OU (kappa: 0.46, p <0.001) and excellent for AP (kappa:0.87, p <0.001). In total, 52.6% of computed tomography were considered unnecessary for NSAP, 82.4% for OU and 91.7% for AP. It was concluded that there are high rates of CT that may be considered unnecessary for the diagnosis of the main emergency conditions, especially appendicitis. The study warns to the exaggerated use of CT in the ER and raise discussions over the possible causes, such as lack of confidence in the clinical diagnosis, fear of diagnostic errors and fear of malpractice lawsuits, of which possible solutions may be more effective when applied since the medical education basis.