This review analyses what is known concerning the immune response of preterm (PTIs) and low birth weight infants (LBWIs) to widely used vaccines, the protection they receive from routine immunisation, and the safety and tolerability of the vaccines themselves. It shows why PTIs and LBWIs should be vaccinated using the same schedules as those usually recommended for full-term infants (FTIs), except in the case of hepatitis B vaccine, whose schedule should be repeated in infants who received the first dose during the first days of life when they weighed less than 2000 g because of their reduced immune response. Vaccines are immunogenic, safe and well tolerated in PTIs and LBWIs, in whom early active immunisation is particularly important because they are among the most vulnerable subjects for pediatric infectious diseases. It is therefore essential to make every effort to convince pediatricians and parents that compliance with these recommendations will not cause any clinical problems.