- Background: Streptococcus pneumoniae conjugate vaccine became available in Costa Rica in 2004. Previous S. pneumoniae middle ear fluid (MEF) data obtained during the period 1999–2001 from Costa Rican children indicated that serotype 19F was the most common type (75%), but more recently other serotypes have become more prevalent. Objectives: To establish the most common S. pneumoniae serotypes present in the MEF of Costa Rican children with otitis media (OM) and to analyze serotype distribution by demographic factors, disease distribution and antimicrobial susceptibility patterns and assess the potential protection provided by the new conjugated heptavalent S. pneumoniae vaccine in Costa Rican children with OM. Methods: During 2002 and 2003, 69 S. pneumoniae isolates were obtained from the MEF of Costa Rican children, ages 3–49 months, with OM. Serotyping was performed by the quellung reaction with antisera from Statens Serum Institute, Copenhagen, Denmark. Results: The most common S. pneumoniae serotypes isolated were 19F (26.1%), 6B (14.5%), 9V (8.7%), 16F (8.7%), 14 (5.8%), 23F (5.8%), 3 (5.8%) and 6A (5.8%). Serotype distribution was similar among children younger than 24 months of age or 24 months of age or older and by disease distribution. There was a tendency towards more penicillin- and trimethoprim-sulfamethoxazole-nonsusceptible isolates among vaccine-type strains than among non-vaccine type strains. Conclusions: The serotype distribution of S. pneumoniae causing pediatric OM in Costa Rica is similar to those reported from developed countries. The current heptavalent pneumococcal conjugate vaccine covers 74% of OM episodes in Costa Rican children.