Introduction: Coronary artery disease (CAD) is one of the most common causes of death worldwide. In 2010, about 7 out of total 53 million deaths were due to ischemic heart disease. The aim of this study is to evaluate the relationship of serum bilirubin level with the severity and complexity of coronary artery disease (CAD) in the patients undergoing primary percutaneous coronary intervention (PCI). Materials and Methods: 70 patients with STEMI who were undergoing primary PCI were included in the study. All the patients included in the study were subjected to full routine investigations and standard coronary angiographic projections. Total bilirubin level was measured and the patients were divided into two groups. Group 1 was with serum TB (<1 mg/dl) and Group 2 was with serum TB (>1 mg/dl). Severity and complexity of coronary artery lesions will be assessed using Gensini score. Results: After PCI, the two studied groups were compared regarding the number of vessels affected by one and more than one vessel disease.