Background Visceral adipose tissue plays a central role in the development of metabolic syndrome (MS). Our study aimed to determine a relationship between MS and subepicardial adipose tissue (SAT), a component of visceral fat surrounding the heart and coronary vessels. Methods A total of 123 patients (54 +/- 10 years of age, 47 male patients) diagnosed with MS and 123 age- and gender-matched control subjects were evaluated echocardiographically. Thickness of the SAT was measured using M-mode echocardiography in parasternal long and short axis views. Maximum values at any site were measured, and the average value was used for statistical analyses. Metabolic syndrome was identified according to the latest criteria of International Diabetes Federation. Results The patients with MS had significantly higher SAT thickness compared to the subjects in the control group (5.1 +/- 1.7 vs. 3.4 +/- 1.6 mm, P < 0.001). A stepwise increase was noted in the SAT thickness depending on the number of the MS components (P < 0.001). The multivariate stepwise linear regression analysis revealed that the diagnosis of MS (t = 3.019, P = 0.001), serum triglyceride level (t = 3.423, P = 0.001), gender (t = -5.507, P < 0.001), age (t = 2.394, P = 0.02) and waist circumference (t = 9.656, P < 0.001) were the independent determinants of SAT thickness. For each 10 and 20-cm increase in waist circumference, 0.094 and 0.19-mm increases in SAT thickness were expected. As an optimal cut off point, 4.35 mm SAT thickness have determined metabolic syndrome with a 61.7% sensitivity and 79.2% specificity. Conclusions A close relationship between SAT thickness and MS was demonstrated. Assessment of SAT thickness in routine echocardiographic examinations might be used in predicting the existence of MS and its associated cardiovascular risks.