Streptococcus pneumoniae is the most frequent cause of otitis media, sinusitis, and pneumonia in children. It is also one of the most common causes of invasive bacterial infections in children including bacteremia and meningitis. One of the current issues regarding S. pneumoniae is the emergence of pneumococcal strains resistant to penicillin and other antibiotics. Children less than two years of age suffer an increased incidence of invasive pneumococcal disease but fail to respond to the 23-valent polysaccharide vaccine because of the immaturity of the T-cell independent immune function. Covalently conjugating the polysaccharide antigen to a carrier protein improves the immune response by permitting the host to utilize a T-cell dependent immune response that is adequately mature in children less than two years of age. Immunogenicity studies of the currently licensed heptavalent conjugated polysaccharide vaccine, (Prevnar, marketed by Wyeth Lederle Vaccines) demonstrated that infants vaccinated with three doses 2 months apart at 2, 4, and 6 months of age successfully developed antibodies to all 7 serotypes; booster doses at 12-15 months demonstrated an amnestic response for each serotype. Immunogenicity studies have similarly demonstrated successful responses in children with sickle cell disease and human immunodeficiency virus infection. An efficacy trial involving nearly 38,000 subjects demonstrated the vaccine's effectiveness in healthy children against invasive pneumococcal disease as well as against pneumonia and otitis media. Currently the US Advisory Committee on Immunization Practices (ACIP) recommends that all infants and children under 24 months of age receive the vaccine. The ACIP recommends that infants receive the vaccine routinely at 2, 4 and 6 months with a fourth dose at 12 to 15 months of age. Infants may receive the first dose as early as 6 weeks of age. The vaccine is also indicated for children 24 to 59 months of age who are at high risk for pneumococcal infection. Adverse events include local reactions in the first two days following vaccination such as approximately 10% reporting erythema, 10% induration, and 20% tenderness. Fever of 38 degrees C or higher occurred in 15% to 25% of children in the first two days following vaccination. Follow-up studies should address important questions regarding the use of pneumococcal conjugate vaccine and other age groups.