BACKGROUND Glycated Hemoglobin (HbA1c) levels are predictive of cardiovascular disease and mortality in patients with diabetes mellitus, however, association of HbA1c with Coronary Artery Disease (CAD) in non-diabetics is inconsistent. OBJECTIVE To evaluate the correlation between HbA1c level and severity of CAD in non-diabetic patients using SYNTAX score in a cohort of proven CAD on angiography at Gauhati Medical College, Guwahati, Assam, India, which is a major tertiary care hospital of North-Eastern India. METHODS We prospectively collected data of non-diabetic patients with proven CAD on angiography from June 2014 to June 2015. Patients were divided into four groups (interquartiles) according to HbA1c levels, less than 4.8%, 4.8% to 5.1%, 5.1% to 5.6%, and 5.6% to 6.5%. Severity of CAD was assessed using SYNTAX score and the number of coronary vessels diseased. We compared different quartiles of HbA1c with regard to SYNTAX score and number of diseased vessels. RESULTS A total of 346 patients were included in the study. Mean age was 58.1±10.4 years. Of the total 91.9% (318) were males, 44.8% (155) were hypertensives, 29.2% (101) were smokers and 34.7% (120) were dyslipidemic. We found that CAD severity by SYNTAX score as well as number of vessels involved was significantly different among quartiles (p-values <0.001 and <0.001 respectively). Increase in HbA1c level was strongly correlated with disease severity and higher SYNTAX score. A significant increase was noted in the mean number of diseased vessels (p-value <0.001) as HbA1c level increases. Age, gender, hypertension and dyslipidemia did not show significant difference among quartiles however smoking was found to be an independent predictor of severity of CAD by SYNTAX score (p <0.05). CONCLUSIONS From this clinical study, we can conclude that a significant correlation exists between HbA1c and severity of CAD by SYNTAX score as well as number of vessels involved in non- diabetes.