Pregnant women with influenza are at increased risk for hospitalization and death. Since 2004, the Advisory Committee on Immunization Practices (ACIP) has recommended inactivated influenza vaccine for all women who are pregnant during influenza season, regardless of trimester. Nonetheless, after the 2004 recommendation, estimated annual influenza vaccination coverage among pregnant women was approximately 15%, before increasing to nearly 50% during the 2009 influenza A (H1N1) pandemic. Since April 2009, CDC has collaborated with state and local health departments to conduct enhanced surveillance for severe influenza among pregnant and postpartum women. To assess maternal and infant outcomes among severely ill pregnant and postpartum women with 2009 H1N1 during the 2009 H1N1 pandemic, CDC analyzed data for the period April 15, 2009 to August 10, 2010. This report summarizes the results of that analysis, which found that, among 347 severely ill pregnant women, 75 died from 2009 H1N1, and 272 were admitted to an intensive-care unit (ICU) and survived. Women who survived received antiviral treatment sooner after symptom onset than women who died. Pregnant women with severe influenza who delivered during their influenza hospitalization were more likely to deliver preterm and low birth weight infants than those in the general U.S. population; infants born after their mother's influenza hospitalization discharge were more likely to be small for gestational age. These data document the severe effects of 2009 H1N1 on pregnant women and their infants, emphasize the importance of vaccinating pregnant women against influenza, and demonstrate the value of prompt administration of antivirals to pregnant women with suspected or confirmed influenza.