We evaluated the Binax NOW Streptococcus pneumoniae urinary antigen assay by testing 210 healthy children aged 2--60 months living in urban slums of Quito, Ecuador. Healthy children with nasopharyngeal carriage of S. pneumoniae were significantly more likely to have positive urinary antigen test results than were children who were not carriers (30 of 138 vs. 3 of 71 children; chi2=10.8; P<.001). The rate of nasopharyngeal carriage of S. pneumoniae decreased with increasing age; the lowest rates were found in children with the worst nutritional status.