OBJECTIVE: The purpose of this study was to evaluate preexisting psychiatric risk factors for postpartum suicide attempts resulting in hospitalization. STUDY DESIGN: We performed a population-based case-control study using Washington State birth certificates linked to hospital discharge data to evaluate the association between hospitalization with a psychiatric diagnosis, substance use diagnosis, or dual diagnosis in the 5 years before delivery with risk of postpartum suicide attempt. We compared cases (n = 355) hospitalized postpartum for a suicide attempt with controls (n = 1420) by using multivariable logistic regression. RESULTS: Women with a psychiatric disorder were at a 27.4-fold (95% confidence interval 10.6-70.8) increased risk, and those with a substance use disorder were at a 6.2-fold (95% confidence interval 2.8-13.9) increased risk, and those with a dual diagnosis were at an 11.1-fold (95% confidence interval 5.1-24.2) increased risk of postpartum suicide attempt compared with controls. CONCLUSION: Prenatal screening for preexisting psychiatric or substance abuse diagnoses may help identify women at risk of postpartum suicide attempt.