Perinatal mental health disorders are increasingly acknowledged as contributors to adverse maternal outcomes. We analyzed data from the Healthcare Cost and Utilization Project National Inpatient Sample (2016 and 2017) to estimate hospitalization cost, length-of-stay, and severe maternal morbidity associated with perinatal mental health disorders overall, as well as stratified by payer and by specific mental health category. We found that people with mental health disorders had $458 higher costs per delivery hospitalization and 50 percent higher rates of severe maternal morbidity compared with people without mental health disorders. We estimated increased annual delivery hospitalization costs of $102 million in the US among people with perinatal mental health conditions compared with those without. Furthermore, people diagnosed with trauma- or stress-related mental health disorders had even higher rates of hospitalization costs-$825 higher per delivery-and 87 percent higher rates of severe maternal morbidity compared with people without those diagnoses. These findings provide important information for perinatal mental health program feasibility and cost-effectiveness analyses and suggest the need for increased focus on trauma- and stress-related disorders.