The epidemiology of red cell transfusion is changing. Surgical use has decreased due to reduced transfusion triggers and better operative techniques. Medical use increases partly due to the increasing age of the population. The evidence for and against transfusion at different levels of anaemia is discussed. The appropriate level of haemoglobin at which to recommend transfusion depends on the indication for transfusion, the patient's co-morbidities and the quality of the red cells available.