Diabetes is a chronic disease characterized by hyperglycemia, and the prevalence of type 2 diabetes is growing to epidemic proportions in certain populations. Type 1 diabetes is primarily the result of autoimmune destruction of beta cells. Type 2 diabetes is found in those with resistance to the action of insulin, usually as a result of obesity, and deficient insulin secretion. Insulin use not only prevents hyperglycemic emergencies, but also is the best safeguard to prevent the long-term complications of diabetes by correcting fasting and postprandial hyperglycemia. Intensive glycemic control can lead to a substantial decrease in the development of microvascular changes found in patients with diabetes. Human insulin analogs, insulins manufactured by recombinant technology which contain substituted or rearranged amino acids, allow more physiological patterns of insulin replacement, termed the basal-bolus approach. Serious hypoglycemia is the biggest obstacle for patients with diabetes treated with intensive insulin programs. Insulin is now available in prefilled pens or can be delivered by a programmable pump to allow greater flexibility in use and to improve glycemic control. Whereas hyperglycemic emergencies are usually treated with intravenous fluids and an intravenous continuous insulin infusion, patients who are less critically ill can be treated with fluid and subcutaneous insulin analogs.