Introduction: COVID-19 is a highly infectious disease spreading all over the world since its appearance causing enormous sufferings and loss of human life specially among those who have suffered from Diabetes Mellitus. Material & method: This retrospective cohort study was conducted among purposively selected 133 COVID-19 patients in which 39 were exposed to DM and 94 were not-exposed to DM who were admitted in CMH, Dhaka from July 2020 to June 2021 with the objective to find out the association of Diabetes Mellitus with the mortality and morbidity outcome of COVID-19 patients within 90 days of discharge from Hospital. The data were collected by telephonic interview and from medical record. Result: The study revealed that the mean age of the respondents were 48.01 years, 80.5% were male. It was seen from the study that among all the respondents 95.5% were survivor and 4.5% were non-survivor. Among the exposed 87.2% were survivor and among the non-exposed 89.9% were survivor. Among the exposed more than half (51.3%) were ⩾60 years age group,48.7% were military retired personnel, 61.5% had family income TK< 25,000. On 14th and 28th day of admission among exposed 94.9% and 30.8% and among non-exposed 83.0% and 21.3% were not cured respectively. Before attaining 28th day of admission among exposed 12.8% and among non-exposed 1.1% were non-survivor. Regarding ICU support among exposed 30.8% and among non-exposed 10.6% required ICU support during treatment, whereas among exposed 33.3% and among non-exposed 6.4% were critical patients. Among exposed 48.7% required oxygen, 17.9% needed ventilator support whereas among non-exposed 23.4% required oxygen and 4.3% needed ventilator support. Among exposed HTN, CHDs and CKDs were 61.5%,7.7% and 12.8% whereas among non-exposed it was 21.3%, 3.2% and 1.1% respectively. The risk exposure outcome among ⩾60 years age group were higher among exposed (RR:2.05, 95% CI 1.33-3.17). Morbidity outcome among exposed on 14th 28th and 90th day were higher (RR:2.05, 95% CI 1.33-3.173), (RR: 1.485, 95% CI 0.847-2.603) and (RR:1.190, 95% CI 0.371-3.820) respectively. Need of Oxygen were higher among exposed (RR:1.445, 95% CI 1.064-1.961). Association in regards to HTN, CHDs and CKD were also higher among exposed which were (RR:1.87, 95% CI 1.321-2.656), (RR: 1.433, 95% CI 0.639-3.214) and (RR:4.394, 95% CI 0.732-26.376) respectively. Conclusion: Health education measures should be taken to prevent and control the morbidity and mortality outcome of COVID-19 patients with special attention to those who are aged, and suffering from DM, HTN and CKD. However, to draw comprehensive inferences on this study, further research on representative sample size in this field is recommended.