4S treptococcus pneumoniae causes a variety of clinical con- ditions, including pneumonia, meningitis, bacteremia and otitis media.This micro-organism is the most common single bacterial agent responsible for respiratory tract infections .Each year, more than one million children are estimated to die each year from pneumococcal pneumonia , half of whom are infants younger than one year of age .Current efforts to prevent mortality and morbidity due to pneumococcal infections in children are focused on early diagnosis and prompt antimicrobial therapy; however, the spread of antimicrobial resistance is leading to the research of new complementary strategies, such as vaccination.Unfortunately, the available 23-valent pneumococcal vaccine is not recommended for children younger than two years of age due to the vaccine's poor immunogenicity.The development of an adequate pneumococcal vaccine for a particular region will depend on the existence of detailed , reliable and representative data on the prevalence and serotype distribution of S pneumoniae.In Latin America , published data on this issue are scarce.Recognizing this problem , the Pan American Health Organization, through its Special Program for Vaccines and Immunization and Sistema Regional de Vacunas , with major