Background Steroids may improve outcomes in high-risk patients undergoing cardiac surgery with the use of cardiopulmonary bypass (CBP). There is a need\ for a large randomized controlled trial to clarify the effect of steroids in such patients. Methods We plan to randomize 7,500 patients with elevated European System for Cardiac Operative Risk Evaluation who are undergoing cardiac surgery with the use of CBP to methylprednisolone or placebo. The first coprimary outcome is 30-day all-cause mortality, and the most second coprimary outcome is a composite of death, MI, stroke, renal failure, or respiratory failure within 30 days. Other outcomes include a composite of MI or mortality at 30 days, new onset atrial fibrillation, bleeding and transfusion requirements, length of intensive care unit stay and hospital stay, infection, stroke, wound complications, gastrointestinal complications, delirium, postoperative insulin use and peak blood glucose, and all-cause mortality at 6 months. Results As of October 22, 2013, 7,034 patients have been recruited into SIRS in 82 centers from 18 countries. Patient's mean age is 67.3 years, and 60.4% are male. The average European System for Cardiac Operative Risk Evaluation is 7.0 with 22.1% having an isolated coronary artery bypass graft procedure, and 66.1% having a valve procedure. Conclusions SIRS will lead to a better understanding of the safety and efficacy of prophylactic steroids for cardiac surgery requiring CBP.