In summary, our review of the literature suggests that diabetes, especially type 1 diabetes, may place patients at risk for a depressive disorder through a biological mechanism linking the metabolic changes of diabetes to changes in brain structure and function. Further studies are warranted examining these relationships in order to better understand the impact of diabetes on brain functioning and structure as well as one potential manifestation of such changes--affective disorder. Moreover, such studies could play a useful role in better understanding mechanisms that commonly underlie the development of depression in individuals without diabetes but with other medical problems or conditions.