BACKGROUND Serum bilirubin is having protective effect as an antioxidant with capacity to remove reactive species of oxygen. Studies have suggested that an increased bilirubin level promotes protection against atherosclerosis. We have evaluated the level of serum bilirubin in patients with suspected coronary artery disease and its correlation with severity of lesion as assessed by modified Gensini score on angiography. MATERIALS AND METHODS A total of 540 patients have been enrolled in the study. Patients with diagnosis of acute coronary syndrome, stable angina, history of typical angina, Treadmill test positive were enrolled in the study. All patients were confirmed to have normal liver and renal function and were taken written consent for coronary angiography. The severity of lesion on angiography was assessed by modified Gensini score. Based on angiography results, the patients have been divided into CAD and control group. RESULTS The no. of patients in CAD group were (n=380) and control group were (n=160). Mean age of presentation in CAD group was 51.40±10.31 yrs. compared to controls 49.80±10.01 yrs. (p=0.1). Males were 70.26% in CAD group and 62.5% in controls (p = 0.08). The serum bilirubin was significantly lower in cases than in controls (0.56±0.28 mg/dL vs. 0.79±0.30 mg/dL, p <0.0001). There was a significant difference between other parameters assessed, i.e. RDW CV (14.46±0.74 vs. 13.72±0.85, p <0.0001), RDW SD (45.61±4.42 vs. 44.41±5.68, p = 0.0086), serum uric acid (7.10±2.06 mg/dL vs. 5.96±1.96 mg/dL, p <0.0001). Univariate analysis have been done followed by multivariate logistic regression analysis for assessing the independent risk factors for CAD. Serum bilirubin, RDW, Sex, Age and Diabetes were found to be independent predictors of presence of CAD. Serum bilirubin negatively correlated with presence of CAD (n=540, r=-0.46, p<0.0001). The cutoff value of serum bilirubin based on Receiver Operating Characteristic curve (ROC) analysis was 0.52 mg/dL for presence or absence of CAD with sensitivity of 80.3% and specificity of 89.1%. The correlation of low bilirubin with severity of CAD was (n=380, r=-0.34). The low serum bilirubin in smokers compared to nonsmokers (both in cases and control groups) did not attain statistical significance. The effect of smoking on level of bilirubin was minimal. CONCLUSION Low Serum bilirubin predicts the presence of CAD and is negatively correlated with the severity of CAD.