BACKGROUND: Empyema is a complication of pneumonia, commonly caused by Streptococcus pneumoniae. AIMS: To validate the utility of an immunochromatographic test for the detection of S. pneumoniae antigen in the pleural fluid of children with empyema. METHODS: Empyema patients had blood and pleural fluid cultured, and polymerase chain reaction (PCR) to detect the S. pneumoniae autolysin gene, lytA, in pleural fluid. Pleural fluid was tested using the Binax NOW S. pneumoniae antigen detection assay and compared with lytA PCR results and/or culture in blood or pleural fluid. RESULTS: S. pneumoniae was detected by PCR in pleural fluid of 68 of 137 (49.6 ) patients, by culture in 11 of 135 (8.1 ) pleural specimens and 16 of 120 (13.3 ) blood specimens. Pleural fluid Binax NOW testing from 130 patients demonstrated a sensitivity of 83.8 and specificity of 93.5 (positive predictive value of 93.4 and negative predictive value of 84.1 ). CONCLUSIONS: In pediatric empyema, high predictive values of pleural fluid Binax NOW S. pneumoniae antigen test suggest that this test may help rationalize antibiotic choice in these patients.