Diabetes mellitus is one of the most frequent metabolic syndromes found in our hospitals, occurring at around 10%. There are basically two types: the most common is Type 2, associated with obesity in almost 80% of cases and family groupings, and then, far behind, comes Type 1 which requires insulin administration for life. Furthermore, there is a condition known as "stress hyperglycaemia" in which a patient without a prior history of diabetes mellitus responds to stress with a syndrome comprising hypermetabolism, hyperglycaemia, hyperlactacidaemia and protein catabolism. The desirable pre-prandial levels of glycaemia in an outpatient are between 80 and 120 mg/dl (under 100 mg/dl is normal) and between 100 and 140 mg/dl before retiring (levels of 110 mg/dl are normal). In patients with artificial nutrition, whether parenteral or enteral, the control of glycaemia is not so strict and the recommendation is for a level of around 150-200 mg/dl in the acute stress phases, falling to 100-150 mg/dl in stable patients. The ideal enteral formula for diabetic patients has been a bone of contention for years and has still not been satisfactorily resolved. The discussion centres on the replacement of saturated fatty acids by mono-unsaturated fatty acids (MUFA) or by carbohydrates. The studies of patients undergoing prolonged treatments with MUFA-rich enteral diets have shown a greater control of glycaemia with these diets than with those rich in carbohydrates, so Type 2 diabetics and in stress hyperglycaemia with enteral nutrition, there is an ever stronger proposal to use MUFA rich formulas, whereas in Type 1 diabetics and in Type 2 patients with high prior requirements of insulin, it would be more recommendable to use diets with a more intermediate composition. With regard to parenteral nutrition, there is a consensus on increasing the amount of fatty acids to the detriment of carbohydrates, but the use of carbohydrates other than glucose is not so clear. The use of fast-acting insulin, either intravenously or subcutaneously, is recommended in the acute stages of the underlying condition because any instability in the patient makes it difficult to plan the required dose of intermediate-acting NPH insulin. The use of metformin or acarbose is not recommended. In parenteral nutrition, the subcutaneous administration of NPH insulin is often required at doses of 30% of the home dosage as the basal insulin therapy in addition to fast-acting insulin in the nutrition bag and a regimen of subcutaneous fast-acting insulin every 6 hours depending on glycaemia.