Streptococcus pneumoniae is a common respiratory pathogen, and up to 50% of children acquire S. pneumoniae in their nasopharynx during the first 12 months of life. The cytokine interleukin-17A (IL-17A) plays an important role in host defense against extracellular bacterial pathogens. We investigated the effect of IL-17 G-152A polymorphism on pneumococcal colonization in children.