The hallmark of glucose‐6‐phosphate dehydrogenase (G6PD) deficiency is red blood cell (RBC) destruction in response to oxidative stress. Patients requiring RBC transfusions may simultaneously receive oxidative medications or have concurrent infections, both of which can induce haemolysis in G6PD‐deficient RBCs. Although it is not routine practice to screen healthy blood donors for G6PD deficiency, case reports identified transfusion of G6PD‐deficient RBCs as causing haemolysis and other adverse events. In addition, some patient populations may be more at risk for complications associated with transfusions of G6PD‐deficient RBCs because they receive RBCs from donors who are more likely to have G6PD deficiency. This review discusses G6PD deficiency, its importance in transfusion medicine, changes in the RBC antioxidant system (of which G6PD is essential) during refrigerated storage and mechanisms of haemolysis. In addition, as yet unanswered questions that could be addressed by translational and clinical studies are identified and discussed.