ABSTRACT With rising rates of opioid use disorder (OUD) in pregnancy, overdose and other complications of OUD have become an increasingly important source of maternal mortality. The postpartum period is a time of particular vulnerability for overdose and other causes of OUD related mortality, but the causes and risk factors for this have not been fully elucidated. Opioid use relapse during the postpartum period may be due to the stresses of new motherhood, loss of insurance, discontinuation of OUD treatment, and opioid analgesic exposure at the time of delivery leading to persistent opioid use and misuse, but data are few. Further, women with OUD may also be particularly vulnerable to other causes of death during the postpartum period including obstetrical complications, suicide, and homicide. There is a need to systematically identify modifiable risk factors that can be the focus of policy and quality improvement initiatives Our group has pioneered the use of pregnancy cohorts nested in the nationwide Medicaid Analytic eXtract (MAX) database to study the safety of medications in pregnancy. The MAX is derived from healthcare utilization claims submitted to the Centers for Medicare and Medicaid Services from all states and Washington, DC. The MAX contains information on patient demographics, inpatient and outpatient diagnoses and procedures, and filled outpatient prescriptions. In the proposed study, we will link the MAX with the National Death Index (NDI), which contains information derived from death certificates including the cause of death. We will then use the linked MAX-NDI database to study the frequency, timing, causes, and risk factors for overdose death and non-overdose deaths in women with OUD. We have assembled an experienced team with extensive expertise in epidemiology, causal inference, substance use disorder, and obstetrics to create this data resource and carry out the proposed Aims. This will not only provide new insight into the epidemiology of overdose and OUD related postpartum death, but also create a powerful new data resource to study maternal mortality generally.