Due to the ways their disease develops diabetics are more likely to require surgery than the rest of the population and operations constitute a stress factor with high rates of morbidity and post-operative mortality due essentially to cardiovascular and infectious complications. In normal subjects the stimulation of the hypothalamohypophyseal axis and the suprarenal marrow induced by surgical stress mobilizes energy substrates that provoke the secretion of insulin that prevents their accumulation and improves their utilization. In diabetics the inadequacy or lack of insulin secretion unbalances these mechanisms to the great danger of the patients themselves. For this reason patients' pre-operative conditions must be very carefully assessed and treatment designed to prevent the increase of catabolic ways due to the lack of insulin must be given. Some of the many treatment protocols proposed are described and discussed, a distinction being made between diet, non insulin and insulin dependent diabetics. The post-operative risk constituted by the onset of non-ketoacidotic hyperosmolar coma, as occurs in other severe stress situations should also be remembered.