Patients with Addison's disease undergoing cardiac surgery are at risk of developing a crisis. There is no consensus on the preoperative and intraoperative management of this group of patients undergoing cardiac surgery so the recommendations for non-cardiac patients are often used. The consensus statement from the international task force of the American College of Critical Care medicine recommends 100 mg of intravenous hydrocortisone for patients with adrenal insufficiency in septic shock, but in patients undergoing surgery, especially with extracorporeal circulation, the dosage may even be higher. We report our management of a patient with well-controlled adrenal insufficiency for 30 years who developed intraoperative Addisonian crisis despite the recommended preoperative corticosteroid supplementation. The importance of adequate corticosteroid supplementation for cardiac surgery patients, adapting the surgical strategy to allow for optimal management of potential complications and close monitoring with heightened awareness are discussed.