Elevated total plasma HOMOCYSTEINE (they) levels constitute a risk factor for coronary artery disease (CAD). A possible relationship was investigated between admission plasma HOMOCYSTEINE level and the angiographic severity and extension of coronary artery disease in patients with CAD. This study looks at the relationship between total plasma HOMOCYSTEINE and severity of coronary artery disease. From April 2006 to December 2006, 100 consecutive patients (65 male and 35 female) that referred to our institute for coronary artery bypass graft surgery enrolled. Fasting blood samples for HOMOCYSTEINE were obtained on admission. Plasma HOMOCYSTEINE concentration was measured with high-performance liquid chromatography (HPLC). Our patients presented in Group 1, total plasma HOMOCYSTEINE >12 micromoles per liter and Group 2, total plasma HOMOCYSTEINE =<12 micromoles per liter. Vessel score assessed the number of vessels with significant stenosis and grading of atherosclerosis (Extent Score) was intended to assess the atherosclerotic involvement of the entire arterial length and circumscribe. Our study was shown age > 60 years was correlated with high they, but gender, hypertension, history of smoking, hypercholesterolemia, family history, and diabetes mellitus were not statistically difference between two groups. A positive correlation was found between abnormal plasma HOMOCYSTEINE level and vessel score (r = 0.35; p=0.002). Moreover, a positive correlation was also found with extent score (r = 0.46; p =0.002). As results of these scoring, there was a better correlation between the they level and the extent of CAD when compared with the vessel score (r = 0.68, p < 0.001). Abnormal elevated HOMOCYSTEINE levels in patients with coronary artery disease correlated with the extent of atherosclerotic disease.