This study assesses the accuracy of Emergency Medicine (EM) residents in detecting the size and presence of abdominal aortic aneurysms (AAAs) using EM ultrasound (EUS) compared to radiology measurement (RAD) by computed tomography (CT) scan, magnetic resonance imaging (MRI), angiography, or operative findings. There were 238 aortic EUS performed from 1999-2000; 36 were positive for AAA. The EUS finding of "AAA" had a sensitivity of 0.94 (0.86-1.0 95% confidence interval [CI]) and specificity of 1 (0.98-1.0 95% CI). Mean aortic diameter among patients with AAA identified by EUS was 5.43+/-1.95 cm and by RAD was 5.35+/-1.83 cm. The mean absolute difference between EUS and RAD diameters was 4.4 mm (95% CI 3.7-5.5 mm). Regression of EUS on RAD diameters is strongly correlated, with R(2)=0.92. EM residents with appropriate training can accurately determine the presence of AAA as well as the maximal aortic diameter.