BACKGROUND Epicardial fat (EF) is the visceral fat of the heart deposited under the visceral layer of the pericardium and has the same origin as abdominal visceral fat, which is shown to be strongly related to the development of coronary artery disease (CAD). We measured the volume of EF (EFV) by 64-multidetector computed tomography (MDCT) and studied the relationship between EFV and the severity of CAD. OBJECTIVE Epicardial fat volume increases steeply in patients with significant coronary artery stenosis and in those with severe coronary artery calcification. METHODS We studied 197 patients with suspected CAD who underwent 64-MDCT and coronary angiography. Cross-sectional tomographic cardiac slices (3.0 mm thick) from base to apex (30 to 40 slices per heart) were traced semiautomatically and EFV was measured by assigning Hounsfield units ranging from -30 to -250 to fat. RESULTS Epicardial fat volume was 99.4 ± 40.0 ml (range, 11.6 to 263.8 mL) and coronary artery calcium score (CACS) was 267.2 ± 605.1 (range, 0 to 3780). There was a significant relationship between EFV and CACS (r=0.210, P=0.003). Patients with EFV >100 had a CACS that was significantly higher than in those with EFV <100 (384.0 ± 782.0 vs 174.8 ± 395.6; P = 0.016). The incidence of significant CAD was significantly higher in patients with EFV >100 compared with those with EFV <100 (40.2% vs 22.7%; P=0.008). The EFV was significantly higher in patients with severe coronary artery stenosis and in those with severe coronary artery calcification (CACS >400). CONCLUSIONS Our results showed that EFV was associated with coronary atherosclerosis, and EFV increased steeply in patients with severe coronary artery stenosis and in those with severe coronary artery calcification.