Although many cases of simultaneous presentation of thyrotoxicosis (thyroid storm) and diabetic ketoacidosis have been reported, it is a clinically unusual situation and remains a diagnostic and management challenge in clinical practice. The diagnosis of diabetic ketoacidosis or thyrotoxicosis may be masked leading to serious complications. We report two patients with simultaneous thyrotoxicosis and diabetic ketoacidosis resulted in sudden cardiac arrest, emphasizing early recognition and prompt treatment when these two disease are presented concomitantly.