Aim: The aim of this study was to examine the levels of serum B12, folic acid, and homocysteine at admission in the cases established at the emer-gency department with thrombo-embolic diseases and to compare them with healthy subjects and also compare the diagnosis groups with each other. Material and Method: This study included 100 subjects diagnosed at the emergency department between March 2009-May 2009 with acute myocardial infarction, acute pulmonary embolism, deep vein thrombosis, ischemic cerebrovascular disease, acute mesenteric embolism, peripheral artery embolism and 110 healthy voluntary subjects were included in the control group. Vitamin B12, folic acid, and homocysteine levels were examined in blood samples obtained at admission. Mann-Whitney U test was used to compare the patient and control group. Kruskal-Wallis variance analysis was used to compare the patient group, according to diagnosis. p≤ 0.05 was considered as significant. Results: Mean serum homocysteine and plasma vitamin B12 levels were significantly higher in the patient group than control group (p=0.002, 0.000 respectively). Mean serum B12 values of acute myocardial infarction and Ischemic Cerebrovascular Disease groups in the patient group were significantly lower than those of the control group (p<0.05). Serum folic acid values of peripheral artery embolism and acute myocardial infarction groups were considerably lower than the control group (p<0.05). Plasma homocysteine levels were significantly higher in all patient groups according to their diagnosis than the control group (p<0.05). Discussion: Serum vitamin B12 and folic acid levels in the acute period of thromboembolic diseases of ST-elevation myocardial infarction, non-ST elevation myocardial infarction, pulmonary embolism, and ischemic cerebrovascular disease are lower than those of other thromboembolic diseases. Plasma homocysteine levels are high during the acute period of all thromboembolic diseases; they are at the highest levels in acute pulmonary embolism, ST-elevation myocardial infarction, and non-ST elevation myocardial infarction which have high morbidity and mortality rates when compared with the other thromboembolic diseases.