Objective To determine risk factors and time to diagnosis of postpartum severe hypertension (PHTN) in women with chronic hypertension (CHTN). Study Design Retrospective cohort of singleton pregnancies with CHTN at a tertiary care center. The primary outcome was PHTN, defined as hypertension ≥160/ ≥ 110 mm Hg during an emergency room (ER) or outpatient visit, or hospitalization within 8 weeks postpartum. Multivariable logistic regression was used to assess independent risk factors for PHTN. Results Two-hundred thirty-five women had CHTN: 30 (12.8%) were diagnosed with PHTN, and 17 (7.2%) were hospitalized or seen in the ER for PHTN. Women with PHTN had more severe superimposed pre-eclampsia (p < 0.05), higher average systolic blood pressures at discharge (141 vs. 135 mm Hg, p = 0.04), and required antihypertensives after delivery (p < 0.01). The number of antihypertensive medications (adjusted odds ratio [aOR] 1.78, 95% confidence interval [CI], 1.25-2.55) and a systolic blood pressure >135 mm Hg (aOR 4.55, 95% CI, 1.64-12.61) at discharge remained independently associated with PHTN. Median time to diagnosis of PHTN was 10 days (interquartile range [IQR] 6-32 days); time to diagnosis among women requiring readmission or ER evaluation was 8 days (IQR 5-11 days). Conclusion PHTN occurred in 13% of women with CHTN, and was associated with blood pressure level and number of medications at discharge.