Among healthy persons, two groups are notable for increased risk of serious illness and hospitalization with influenza infection: healthy women in pregnancy and their healthy infants (aged 0 to 6 months). Inactivated influenza vaccine has been used in pregnant women since the 1960s in both the United States and Canada; however, currently, only 15% of pregnant women receive the vaccine. A randomized, controlled trial has shown influenza immunization of pregnant women reduced influenza-like illness by more than 30% in both the mothers and the infants and reduced laboratory-proven influenza infections in 0- to 6-month-old infants by 63%. Physicians caring for pregnant women should be aware of the risks of influenza and of the availability of an effective and cost-saving intervention.