Problem: This literature review will aim to discuss the association between depression and diabetes mellitus and the impact depression can have on diabetes mellitus outcomes. Furthermore, it will explore impacts the treatment of depression may have on the course of diabetes mellitus type 2 (DM II) with particular attention paid to objective measurements such as HbA1c levels. This review should provide healthcare practitioners with an understanding that diabetics suffer from increased rates of depression and that depression can negatively impact the course of DM II as evident by observations of increased incidence of co-morbidities and poorer glycemic control. Methods: Using the PubMed database provided by the Weill Cornell Medical College Library online, relevant studies were identified using search terms such as, "diabetes" AND "depression," "depression AND glycemic control," "depression AND HbA1c," "mental illness AND diabetes," "mental illness AND hyperglycemia," "depression AND chronic illness," and "SSRI AND hyperglycemia." Results: Twenty-one articles were located for the review. Seven articles were excluded due to a narrow focus, lack of clear presentation, too broad of a research topic, low reliability a small study size and a subject matter that did not pertain to the research at hand. In total, 14 articles were reviewed. Conclusions: Upon review of the literature, it is apparent that strong associations exist between diabetes mellitus and depression. This relationship appears to be bidirectional with diabetes increasing the risk of depression, while depression increases the risk of diabetes onset and a less favorable outcome.