Streptococcus pneumoniae is the most common cause of community-acquired pneumonia but is undoubtedly underdiagnosed. Isolation of S. pneumoniae from blood is specific but lacks sensitivity, while isolation of S. pneumoniae from sputum may represent colonization. We evaluated a new immunochromatographic test (NOW S. pneumoniae urinary antigen test; Binax, Portland, Maine) that is simple to perform and that can detect S. pneumoniae antigen in urine within 15 min. Urine samples from 420 adults with community-acquired pneumonia and 169 control patients who did not have pneumonia were tested. Urine from 315 (75%) of the pneumonia patients and all controls was tested both before and after 25-fold concentration, while the remaining 105 samples were only tested without concentration. S. pneumoniae urinary antigen tests were positive for 120 (29%) patients with pneumonia and for none of the controls. Of the urine samples tested with and without concentration, 96 were positive, of which 6 were positive only after concentration. S. pneumoniae antigen was detected in the urine from 16 of the 20 (80%) patients with blood cultures positive for S. pneumoniae and from 28 of the 54 (52%) patients with sputum cultures positive for S. pneumoniae . The absence of S. pneumoniae antigen in the urine from controls suggests that the specificity is high. Concentration of urine prior to testing resulted in a small increase in yield. The NOW S. pneumoniae urinary antigen test should be a useful adjunct to culture for determining the etiology of community-acquired pneumonia in adults.