Diabetes mellitus is a worldwide highly prevalent chronic metabolic disorder, characterized by hyperglycemia, and is associated with significant complications, including the microvascular complications such as neuropathy, retinopathy and nephropathy and the macrovascular complications such as cardiovascular, cerebrovascular disease and peripheral vascular disease, thus leading to significant morbidity and mortality. Patients with diabetes were found to be 1.4-3 times more likely to suffer from comorbid depression when compared to non-diabetics, and depression in diabetes is usually persistent and/or recurrent. Depression was found to be increased among patients with type I and type II diabetes mellitus, which have higher glycosylated hemoglobin. Association was also found between diabetic complications and depression, and this relation is bidirectional since depression might be linked to poor glycemic control and complications lead to negative impact on patients’ physical and mental health and leads to worse quality of life, thus fostering the development of depression. The presence of depression by itself was found to be associated with significant negative impact in their diabetes self-care and having proper glycemic control, and led to worse health outcomes and quality of life. Thus, American Diabetes Association currently recommends that patients with diabetes mellitus, especially those with poor glycemic control, should be screened for depression.