Objective: Admissions to acute care hospitals represent a significant portion of healthcare utilization. Little is known regarding hospitalization in the first postpartum year beyond the traditional 6 weeks of the puerperium. We sought to investigate whether there are identifiable risk factors for hospital readmission during this time period. Study Design: We conducted a retrospective population-based study using all California birth records between 1999 and 2003. These records were linked with hospital discharge data for all admissions to California hospitals in the first 365 days after delivery. For women with a first birth during the study period, we assessed the likelihood of readmission to an acute care hospital between 42 and 365 days post-delivery. Univariate and multivariable logistic regression were used to determine risk factors for these “late postpartum” admissions. Results: Of 951,570 maternal birth admissions during the time period, 15,727 (1.7%) women were admitted in the late postpartum period. Women with an early postpartum readmission, antepartum admission, extremes of maternal age, black race, diabetes, hypertension, early preterm delivery and cesarean delivery had higher rates of late postpartum readmission. Of women with an antepartum admission for gestational diabetes or pre-existing diabetes, 6.6% and 18.5% of these women experienced a late postpartum admission for a diabetes-related diagnosis. Conclusion: Hospital readmission rates in the first year postpartum, remote from delivery, are significant. Women are at a higher risk of requiring hospital admission in the first year postpartum with select demographics and pregnancy-related diagnoses.