Objective: To determine whether pregnant women with brain tumors have an elevated risk of adverse pregnancy outcomes. Background Diagnosis of a brain tumor during pregnancy presents complex management challenges, and relevant population-based studies are lacking. Design/Methods: We designed a retrospective cohort study using the Nationwide Inpatient Sample (NIS), a stratified sample of US hospitalizations, to investigate pregnancy outcomes in women with brain tumors. We constructed a logistic regression model for the outcomes of maternal mortality, preterm labor, Caesarean delivery, miscarriage, and elective abortion, controlling for age, medical comorbidities, and demographic and hospital characteristics. Results: We identified 379 malignant and 437 benign brain tumors among 19 million pregnancy-related admissions between 1988 and 2009. Malignant brain tumors were associated with maternal mortality (OR 143), miscarriage (OR 1.8), and elective abortion (OR 11.6). Caesarean delivery was more frequent for malignant (OR 5.3) and benign (OR 2.2) brain tumors. Admissions not resulting in a delivery were more common for malignant (OR 8.6) and benign (OR 4.3) brain tumors. As with non-pregnant adult brain tumor patients, seizures (16%) and hydrocephalus (6%) were the most common associated diagnoses. Hyperemesis gravidarum was more common for malignant (OR 2.2) and benign (OR 2.8) brain tumors, raising the suspicion that elevated intracranial pressure was responsible for symptoms thought to be pregnancy-related. 27% of all hospitalizations involved a neurosurgical procedure, but the likelihood of pregnancy complications was not significantly increased in these patients. All reported associations were statistically significant to a level of p Conclusions: Brain tumors are strongly associated with adverse pregnancy outcomes, but neurosurgery during pregnancy does not appear to enhance these risks. Brain tumors were associated with higher rates of Caesarean delivery, implying a conservative management strategy. Further research is needed to improve understanding of obstetric risk in this patient population and to assist with treatment, prenatal counseling, and monitoring during delivery. Supported by: Harvard Center for Neurofibromatosis and Allied Disorders. Disclosure: Dr. Terry has nothing to disclose. Dr. Barker has nothing to disclose. Dr. Leffert has nothing to disclose. Dr. Bateman has nothing to disclose. Dr. Souter has nothing to disclose. Dr. Plotkin has received research support from Pfizer.