Objective: To estimate whether severe maternal morbidity is associated with increased risk of psychiatric illness in the year after delivery hospital discharge. Methods: This retrospective cohort study used International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM) codes within Florida's Healthcare Cost and Utilization Project's databases. The first liveborn singleton delivery from 2005 to 2015 was included; women with ICD-9-CM codes for psychiatric illness or substance use disorder during pregnancy were excluded. The exposure was ICD-9-CM codes during delivery hospitalization of severe maternal morbidity, as per the Centers for Disease Control and Prevention. The primary outcome was ICD-9-CM codes in emergency department encounter or inpatient admission within 1 year of hospital discharge of composite psychiatric morbidity (suicide attempt, depression, anxiety, posttraumatic stress disorder, psychosis, acute stress reaction, or adjustment disorder). The secondary outcome was a composite of ICD-9-CM codes for substance use disorder. We compared women with severe maternal morbidity with those without severe maternal morbidity using multivariable logistic regression adjusting for sociodemographic factors and medical comorbidities. Cox proportional hazard models identified the highest risk period after hospital discharge for the primary outcome. Results: A total of 15,510 women with severe maternal morbidity and 1,178,458 without severe maternal morbidity were included. Within 1 year of hospital discharge, 2.9% (n=452) of women with severe maternal morbidity had the primary outcome compared with 1.6% (n=19,279) of women without severe maternal morbidity, resulting in an adjusted odds ratio (aOR) 1.74 (95% CI 1.58-1.91). The highest risk interval was within 4 months of discharge (adjusted hazard ratio [adjusted HR] 2.53 [95% CI 2.05-3.12]). Most severe maternal morbidity conditions were associated with higher risk of postpartum psychiatric illness. Women with severe maternal morbidity had nearly twofold higher risk of postpartum substance use disorder (170 [1.1%] vs 6,861 [0.6%]; aOR 1.91 [95% CI 1.64-2.23]). Conclusion: Though absolute numbers were modest, severe maternal morbidity was associated with increased risk of severe postpartum psychiatric morbidity and substance use disorder. The highest period of risk extended to 4 months after hospital discharge.