Diabetes mellitus, defined as a fasting plasma glucose of >126 mg/dL measured on two separate occasions, reflects the inability of the body to produce or respond properly to insulin. Even when glucose levels are considered to be "well controlled," diabetes increases the risk of stroke one to three times above that of people without the disease. It is important to identify patients who are diabetic and to treat their diabetes (which will significantly reduce their risk of many other vascular complications of diabetes). However, since diabetes puts these patients at high risk for stroke, it is particularly important to control any additional risk factors for stroke (such as hypertension and hyperlipidemia) that they may have.

Populations at special risk
Mexican Americans and African Americans have almost twice the risk of diabetes as non-Hispanic whites. The risk for American Indians is even higher.

Relationship to stroke pathogenesis
Diabetes increases the risk of ischemic strokes through several interrelated mechanisms that favor (and accelerate) the formation of atherosclerotic plaques  In patients with diabetes, plaque formation is much more common in the smaller branches of cerebral arteries than in nondiabetics. The narrowing of these smaller vessels can directly increase the risk of stroke.