Although early cardiac computed tomographic angiography (CCTA) might improve the management of emergency department (ED) patients with acute chest pain, it could also result in increased testing, costs, and radiation exposure. ROMICAT II was a randomized comparative effectiveness trial enrolling patients 40 to 74 years old without known coronary artery disease who presented to the ED with chest pain but without ischemic electrocardiographic (ECG) changes or elevated initial troponin and who required further risk stratification. Overall, 1000 patients at 9 sites within the United States were randomized to either CCTA as the first diagnostic test following serial biomarkers or to standard of care, which included no testing or functional testing such as exercise ECG, stress radionuclide imaging, or stress echocardiography. Test results were provided to ED physicians, yet patient management was not driven by a study protocol in either arm. Data were collected on diagnostic testing, cardiac events, and cost of medical care for the index hospitalization and during the following 28 days. The primary end point was length of hospital stay. Secondary end points were cumulative radiation exposure, resource utilization, and costs of competing strategies. Tertiary end points were institutional, physician, and patient characteristics associated with primary and secondary outcomes. Rate of missed acute coronary syndrome within 28 days was the safety end point. The ROMICAT II will provide rigorous data on whether CCTA is more efficient than standard of care in the management of patients with acute chest pain at intermediate risk for acute coronary syndrome.