Objective: To describe the prevalence of hospitalizations during pregnancy, the reason for hospitalization, the length of stay, and the associated costs. Methods: We analyzed data from a national managed care organization and determined the occurrence of hospitalizations for 46,179 women who had a live birth or a pregnancy loss in 1997. Results: Overall, 8.7% of women were hospitalized during their pregnancy. Of these, 5.7% were hospitalized and discharged while pregnant, 0.8% experienced extended stays before a live birth or pregnancy loss, and 2.1% experienced pregnancy loss. Hospitalizations were more common among younger women, women with multiple gestations, and women in the northeastern United States. Women who had a live birth were primarily hospitalized for preterm labor (24%), hyperemesis (9%), hypertension (9%), kidney disorders (6%), and prolonged premature rupture of membranes (6%). Charges totaled over $36 million. Conclusion: Antenatal hospitalizations are common.