Objective: To estimate characteristics and outcomes of pregnant and immediately postpartum women hospitalized with influenza-like illness during the 2009-2010 influenza pandemic and the factors associated with more severe illness. Methods: An observational cohort in 28 hospitals of pregnant and postpartum (within 2 weeks of delivery) women hospitalized with influenza-like illness. Influenza-like illness was defined as clinical suspicion of influenza and either meeting the Centers for Disease Control and Prevention definition of influenza-like illness (fever 100.0°F or higher, cough, sore throat) or a positive influenza test. Results: Of 356 women meeting eligibility criteria, 35 (9.8%) were admitted to the intensive care unit (ICU) and four (1.1%) died. Two hundred eighteen women (61.2%) were in the third trimester and 10 (2.8%) were postpartum. More than half (55.3%) were admitted in October and 25.0% in November with rapidly decreasing numbers thereafter. Antiviral therapy was administered to 10.1% of the women before hospitalization and to 88.5% during hospitalization. Factors associated with an increased likelihood of ICU admission included cigarette smoking (29.4% compared with 13.4%; odds ratio [OR] 2.77, 95% confidence interval [CI] 1.19-6.45) and chronic hypertension (17.1% compared with 3.1%; OR 6.86, 95% CI 2.19-21.51). Antiviral treatment within 2 days of symptom onset decreased the likelihood of ICU admission (31.4% compared with 56.6%, OR 0.36, 95% CI 0.16-0.77). Conclusion: Comorbidities, including chronic hypertension and smoking in pregnancy, increase the likelihood of ICU admission in influenza-like illness hospitalizations, whereas early antiviral treatment may reduce its frequency. © 2011 by The American College of Obstetricians and Gynecologists. Published by Lippincott Williams & Wilkins.