Despite the success of the national childhood vaccination program in the United States in decreasing mortality due to vaccine-preventable diseases, vaccination rates remain suboptimal. Contributing factors include the failure to appreciate the hazards of vaccine-preventable diseases, concerns about adverse reactions associated with vaccine administration, and missed opportunities to administer vaccines. The 2 major types of indications for vaccinating children are age and presence of a medical condition that increases the risk of a vaccine-preventable disease. Hepatitis B virus (HBV) infection becomes chronic in 90% of those infected as infants, and 25% of those so infected will die of related chronic liver disease as adults. Routine infant vaccination against hepatitis B has been recommended since 1991. Approximately 69% of infants who develop pertussis require hospitalization. Acellular pertussis vaccines have been licensed for use in infancy. Starting in 2000, the all-inactivated poliovirus vaccine (IPV) schedule is recommended. IPV should eliminate vaccine-associated paralytic poliomyelitis. Pneumococcal conjugate vaccine was licensed in 2000 for routine use on a schedule of 2, 4, 6, and 12 to 15 months. The first dose of measles-mumps-rubella vaccine is now recommended at age 12 to 15 months, simultaneous with varicella vaccine administration.