Introduction/ Background: Diabetes mellitus (DM) has emerged as a modern epidemic and is at raising trend globally and will continue to be in the future. Cardiovascular complications are a major cause of death in patients with type II DM. This study was undertaken to find the relationship between HbA1c levels with mortality, morbidity,and severity in patients with Acute Coronary Syndrome(ACS). Objective: To find the relationship between HbA1c levels with mortality, morbidity,and severity in patients with ACS. Material and Method: Prospective observational study was undertaken in Rohilkhand Medical College and Hospital, Bareilly including 100 patients in the medical wards from 1st Jan 2018 to 31st dec 2018. Detailed clinical examination, routine investigations including HbA1c were done. The data was computed and was statistically analyzed. Results: Out of 100 patients, 58 were non–diabetic, 27 were diabetic and 15 had impaired glucose tolerance. 50 patients had dyslipidemia, of which 70% of patients with diabetes had dyslipidemia whereas 50% of impaired glucose tolerance and 41% of non–diabetic patients had dyslipidemia. Dyslipidemia was common in diabetic patients as compared to non–diabetics. 27 patients out of 100 patients had complications of which 12 were non–diabetics, 11 were diabetics while4 had impaired glucose tolerance. The patients with complication had higher mean HbA1c level . (7.14 ± 1.88 in patients with complications as compared 5.56 ± 1.30 in patients without complications) In Coronary Artery Angiography(CAG), multivessel disease involvement was significantly more in diabetics as compared to nondiabetic.( the mean HbA1c was found to be significantly more in patients with the multivessel disease compared to those without multivessel disease). Conclusion: ACS can be the initial presentation of DM i.e patients of DM can have macrovascular complications of diabetes without having the usual symptoms of DM. HbA1c may be a useful indicator for Coronary Artery Disease(CAD) risk evaluation. HbA1c should be used as a measure to label a patient as diabetic in patients of ACS over blood sugar levels. Patients with DM, when compared to non–diabetics, have increased morbidity and severity after an ACS