Background: Diabetes mellitus and essential hypertension are chronic medical conditions that place a lot of burden on patients. The presence of co-morbid depression, suicidal behaviour and impaired quality of life may compound the problems, leading to poor prognosis. Objective: This study assessed the prevalence of depression, suicidal behaviour, quality of life and the socio-demographic correlates among subjects with diabetes mellitus and compared them with subjects with essential hypertension. Method: A total of 540 subjects, 270 each for diabetes mellitus and essential hypertension were interviewed. Consecutive and consenting subjects with diabetes mellitus and essential hypertension that met the inclusion criteria were recruited from the endocrinology and cardiology clinics in University of Nigeria Teaching Hospital Enugu. A socio-demographic questionnaire was used to assess the socio-demographic characteristics. Major depressive episode of Mini-International Neuropsychiatric Interview (M.I.N.I.) and Beck Depression Inventory were used to assess depression while the suicidality module of M.I.N.I. was used to assess suicidal behaviour. The World Health Organization Quality of Life-Bref (WHOQoL-Bref) was used to assess quality of life. Results: The prevalence of depression for the subjects with diabetes mellitus was 27.8% and 26.7% for those with essential hypertension. The subjects with diabetes mellitus had prevalence of 6.3% for suicidal behaviour while those with essential hypertension had 7.8%. The subjects with diabetes mellitus had been significantly ill for a longer duration compared to the subjects with essential hypertension. The subjects with essential hypertension had significantly higher quality of life scores in physical health, psychological well-being and social relationship domains. Depression was more likely in subjects with diabetes mellitus if they were not married or had no formal education while the subjects with essential hypertension were more likely to have depression if they were not married, had no formal education or not employed. Suicidal behaviour was more likely in subjects with diabetes mellitus if they had no formal education while in those with essential hypertension suicidal behaviour was more likely in females, those not married and those not educated. Males, married, educated and employed subjects with diabetes mellitus scored higher on the WHOQoL-Bref while males, married and educated subjects with essential hypertension had higher scores. Conclusion: Depression, suicidal behaviour and impaired quality of life may co-occur with diabetes mellitus and essential hypertension. The negative impact of these co-occurrences on achieving good glycaemic and blood pressure control calls for screening for these conditions when indicated. This may enhance early detection and treatment