OBJECTIVE The aim of this study was to evaluate the effectiveness of computed tomography (CT) attenuation values in the characterization of pericardial effusion. METHODS This study consisted of 96 patients with pericardial effusion who underwent pericardiocentesis. For further diagnostic evaluation of pericardial effusion, all the patients were assessed by thorax CT. CT attenuation values were measured from at least 5 different areas of pericardial fluid by specifying the largest region of interest. The average of these measurements was computed and considered as the CT attenuation value of the patient. The patients were classified into two groups: patients with transudative pericardial effusion and those with exudative pericardial effusion. RESULTS CT attenuation values were significantly higher in patients with exudative pericardial effusion than in those with transudative pericardial effusion [14.85±10.7 Hounsfield unit (HU) vs. 1.13±4.3 HU, p<0.001]. CT attenuation values had a close correlation with the pericardial fluid albumin (r=0.829), protein (r=0.752), and LDH (r=0.708) levels; WBC count (r=0.564); protein ratio (r=0.739); and LDH ratio (r=0.689) as well as the albumin gradient (r=-0.725). A cut-off value of 4.7 HU had 80% sensitivity and 87.7% specificity for the identification of exudative pericardial effusion. In addition, a cut-off value of 6.5 HU had 71.4% sensitivity and 72.3% specificity for the prediction of cardiac tamponade. CONCLUSIONS In patients with pericardial effusion, CT attenuation values seem to be correlated with the characterization parameters of the fluid and may distinguish exudative pericardial effusion from transudative pericardial effusion. This parameter was also found to be a predictor of cardiac tamponade. CT attenuation values can be a useful tool in the clinical evaluation of patients with pericardial effusion.