Diabetic coma is a life-threatening but reversible form of coma found in people with diabetes mellitus.

Three different types of diabetic coma are identified:

1. Severe low blood sugar in a diabetic person
2. Diabetic ketoacidosis (usually type 1) advanced enough to result in unconsciousness from a combination of a severely increased blood sugar level, dehydration and shock, and exhaustion
3. Hyperosmolar nonketotic coma (usually type 2) in which an extremely high blood sugar level and dehydration alone are sufficient to cause unconsciousness.

In most medical contexts, the term diabetic coma refers to the diagnostical dilemma posed when a physician is confronted with an unconscious patient about whom nothing is known except that they have diabetes. An example might be a physician working in an emergency department who receives an unconscious patient wearing a medical identification tag saying DIABETIC. Paramedics may be called to rescue an unconscious person by friends who identify them as diabetic. Brief descriptions of the three major conditions are followed by a discussion of the diagnostic process used to distinguish among them, as well as a few other conditions which must be considered.

An estimated 2 to 15 percent of people with diabetes will have at least one episode of diabetic coma in their lifetimes as a result of severe hypoglycemia.