BACKGROUND: Pericardial fat volume (PFV), defined as the volume of ectopic fat in and around the heart, is associated with the atherosclerotic process in coronary arteries. The magnitude of change in PFV over time and the factors affecting this change in a general population, however, have not been investigated. Methods and Results: Cardiac computed tomography (CT) was carried out at baseline and at follow-up in 623 Japanese men aged 40-79 years without a history of cardiovascular disease who were selected randomly in Kusatsu (Shiga, Japan). PFV was measured on cardiac CT in a qualified laboratory. Age, heart rate, triglycerides, and obesity measurements (weight, body mass index, and waist circumference) were significantly and positively associated with PFV at baseline. Over an average interval of 4.7 years, median PFV increased significantly from 64.1 cm3 (IQR, 47.2-90.0 cm3) to 73.6 cm3 (IQR, 53.3-98.1 cm3; P<0.001). Current smoking and heart rate were significantly and independently associated with changes in PFV (B=3.336, P<0.001 and B=6.409, P=0.003, respectively). CONCLUSIONS: PFV increased significantly over time in a population-based observational study of Japanese men. PFV change was significantly and independently associated with smoking status and heart rate, suggesting that quitting smoking might help reduce PFV, which could be expected to decrease the risk of coronary artery disease.