From a complications standpoint, diabetes mellitus is a disease of the vasculature. Diabetics face a considerably higher risk of developing cardiovascular and cerebrovascular diseases. Both large and small blood vessels are susceptible to alterations from diabetes. Endothelial cell dysfunction associated with small vessel (known as microangiopathy) is a primary factor in the development and progression of diabetes-related disabilities, including blindness, kidney failure, and peripheral neuropathy. Recent clinical evidence show that people with diabetes have increased incidences of vascular dementia, ventricular hypertrophy, lacunar infarcts, hemorrhage, and may be a predisposing factor for Alzheimer's disease. However, the effects of diabetes mellitus on the cerebral microvascular are still largely unknown. This communication will review the relationship between diabetes mellitus and changes in cognition with a particular focus on how alterations in blood-brain barrier structure and function may play a long term role in worsened cognitive abilities.