Cardiac surgery involving cardiopulmonary bypass (CPB) in its conventional form involves many processes leading to free radical production, such as perioperative ischemia, reperfusion, circulation of whole body blood through the CPB circuit, hypothermia and acidosis. The red blood cells of a glucose-6-phosphate dehydrogenase (G6PD)-deficient person are unable to scavenge these free radicals, resulting in haemolysis. Here, we describe the successful anaesthetic management of two G6PD-deficient children who underwent cardiac surgery, on and off CPB, without any obvious haemolytic reaction, followed by a discussion of the disorder, with specific consideration of perioperative management of such cases.