Introduction: Breast cancer (BCa) is the second leading cause of cancer in women . Estrogen exposure is an established risk factor for developing BCa. Hypertensive disorders of pregnancy (HDP) have been associated with hormonal changes that could lead to lower BCa risk including lower estrogens and insulin-like growth factor I (IGF-I). Therefore, we sought to investigate whether or not a history of HDP reduces the risk of BCa. Methods: The cohort consisted of women who delivered between January 1, 1976–December 31, 1982 while residents of Olmsted County, Minnesota, without a prior history of HDP. Pregnancies were classified as normotensive, gestational hypertension, preeclampsia, eclampsia, and chronic hypertension using a validated electronic algorithm. For each woman with a pregnancy complicated by HDP, we randomly identified 2 referent women from the cohort matched on delivery date, maternal age, and parity at index pregnancy who had not met criteria for HPD by that delivery date. Incident BCa diagnoses were first identified using diagnostic codes electronically pulled from the Rochester Epidemiology Project (REP) medical record system, and then manually reviewed and confirmed by a clinician. Due to the lower event rate of BCa among parous women compared to the general population, the study was powered to detect a hazard ratio (HR) <0.47. Follow-up was calculated from index date to the date of BCa diagnosis, or last visit to a REP-affiliated provider. Chi-squared tests were used to measure the differences between nominal variables. Cox proportional hazards models were fit to estimate HRs and corresponding 95% CIs using age as the time scale. Results: After manual review, there were 570 women with an HDP complicated pregnancy along with 1140 matched referent women. Average follow-up time was 29.5 y for women with an HDP and 26.7 y for referent women. There were 63 with BCa during follow-up. There was no statistical difference between patient or tumor characteristics, and clinical stage between the two groups (Table 1). HDP was associated with a reduced risk of BCa; however, results were not statistically significant (HR 0.77, 95% CI 0.45-1.32; P=0.39). Discussion: We performed a large population-based matched cohort analysis of parous women with and without HDP and found a decreased but nonsignificant risk of subsequent BCa diagnosis. Therefore, molecular targets of known HDP pathways could be investigated for prevention or treatment of BCa.