In contrast to pleural effusion or ascites, there are few data regarding the chemical and cell-count parameters of pericardial effusions (PEs) to aid diagnosis. In the present work, all patients who underwent pericardiocentesis during a 9-year period (1995 to 2004) at a tertiary hospital and who had available fluid laboratory results were retrospectively identified. Causes of PE were diagnosed using predetermined criteria. The results of pericardial fluid biochemical and hematologic tests were compared with blood test results and analyzed to identify cut-off points that could distinguish among the various causes or among various groups of causes. Of 173 patients who underwent pericardiocentesis in the study period, 120 had available fluid laboratory results, and these patients constituted the study population. The most common causes of PE were neoplastic, idiopathic, and effusion related to acute pericarditis (accounting for 42, 22, and 17 of 120 patients, respectively). Most fluids (118 of 120) would have been classified as exudates by adopting Light's pleural effusion criteria. Moreover, in all parameters examined, there was a considerable overlap of test results among the different pericardial disorders. Thus, no biochemical or cell-count parameter was found useful at reasonable accuracy for differentiating among the individual causes or among various groups of pericardial disorders. In conclusion, most PEs are exudates. The analysis of pericardial fluid biochemical and cell-count composition is generally not helpful for the diagnosis of most PEs.