The Jordanian population has high rate of coronary artery disease (CAD). The potential association between deficiency of vitamin B12, folic acid, and hyperhomocysteinemia in patients with acute myocardial infarction (AMI), where investigated. A case-control study was carried out involving 210 AMI patients (age 35-70 years; 160 men and 50 women) and 100 normal healthy individuals (age 35-70 years; 70 men and 30 women). Fasting venous blood was obtained from patients and controls. Serum was analyzed for vitamin B12 and folic acid using radioassays. The mean serum B12 concentration in AMI patients was found to be significantly lower in controls. The mean serum folate level in patients was also found to be lower than in controls. On the contrary, plasma homocysteine level in AMI patients was higher than that in controls, but not significantly. However, the homocysteine in normal healthy controls was greater than what had been reported in the literature. Vitamin B12 and folate deficiency in AMI patients was significantly higher than in controls. Plasma levels of homocysteine in smokers were also significantly higher in both patients and controls. Additionally, smokers had significantly lower serum folate levels than nonsmokers. Vitamin B12 and folate deficiency in association with hyperhomocysteinemia may be considered as a risk factor for CAD development.