Acute kidney injury, a common complication of cardiac surgery with cardiopulmonary bypass, is associated with increased morbidity and mortality. Ischemic preconditioning at a remote site mitigates ischemia-reperfusion injury and may prevent acute kidney injury after cardiac surgery, thus providing clinical benefit. To further study this, we enrolled 120 adult patients undergoing elective cardiac surgery for whom cardiopulmonary bypass was anticipated in a randomized, single-blind, and controlled pilot trial. Patients were stratified for the type of surgery and equally assigned to a control group or to receive remote ischemic preconditioning by an automated thigh tourniquet consisting of three 5-min intervals of lower extremity ischemia separated by 5-min intervals of reperfusion. The primary end point was acute kidney injury defined as an elevation of serum creatinine of ≥0.3 mg/dl or ≥50% within 48 h after surgery. Fifty-nine patients in each group were analyzed on an intention-to-treat basis. Acute kidney injury occurred in 12 remote ischemic preconditioned and 28 control patients, reflecting an absolute risk reduction of 0.27 and a significantly reduced relative risk due to preconditioning of 0.43. Hence, remote ischemic preconditioning prevents acute kidney injury in patients undergoing cardiopulmonary bypass-assisted cardiac surgery.