Title: The association between newly diagnosed Type 2 Diabetes Mellitus and Depression: a hospital based, cross-sectional study in Chennai, India. Background: The prevalence of Type 2 Diabetes Mellitus and Depression are increasing globally, both as separate entities and as co-morbid conditions. Approximately 382 million people have Type 2 Diabetes Mellitus and 350 million have depression worldwide. Research has established the bi-directional relationship between the two conditions and studies have reported significantly higher rates of depression in patients with T2DM compared to those without. Increasing prevalences of both T2DM and Depression in the South-Asian population is a growing concern as both conditions are debilitating and bring the worst outcomes as co-morbid conditions. These findings are however limited in the South-East Asian region and need to be further investigated. Objective: The main objective of the study was to assess the prevalence of depression in newly diagnosed Type 2 Diabetes Mellitus and the relationship between the two conditions and to identify other factors that may be associated with depression. Methods: The prevalence of unrecognized depression and undiagnosed Type 2 Diabetes and their association was assessed in Chennai, India using a cross-sectional design. Information on socio-demographic details, biochemical parameters and anthropometry were collected. Depression was assessed using MADRS before the results of diabetes was made known to the subjects and investigator. Results: The study could not achieve the calculated sample size of 243. A total of 145 subjects participated in the study. The prevalence of newly diagnosed Type 2 Diabetes Mellitus was found to be 22.8% (25.6% among males and 19.0% among females). According to MADRS, the prevalence of depression was found to be 28.3% (20.7% among males and 38.1% among females). The prevalence of depression in the newly diagnosed diabetic subjects was 33.3%. Diabetes was found to have no association with depression in the present study. Only the divorced/widowed category of civil status had a significant association with depression after adjusting for both confounders and other competing exposures. Conclusion: A high prevalence of both depression and Diabetes was found in the present study. The proportion of depression in newly diagnosed diabetes was very high in this study population. Diabetes was not found to be a strong risk factor for depression, possibly because of the lack of statistical power. There is a need for further studies to investigate the etiology between Diabetes and depression. The results from the present study may indicate the need for regular screening for early diagnosis of the conditions and implementing preventive and treatment strategies aiming at the comorbidity of depression and Type 2 Diabetes Mellitus.