The purpose of this study was to determine if women with preeclampsia are more likely to have a sister who also had preeclampsia. Study design: This was a population-based case-control study using data from Washington (WA) state birth certificates linked to hospital discharge records. Cases were women with gestational hypertension (n = 1611) or preeclampsia (n = 1071); controls (n = 8041) had normotensive pregnancies. All women delivered their first child between 1987 to 2002 and had a sister with a previous delivery in WA. Results: Women with preeclampsia were 2.3 times (95% CI 1.8- 2.9) more likely to have a sister who had preeclampsia; those with gestational hypertension were 1.6 times (95% CI 1.3- 2.0) more likely to have a sister with gestational hypertension. Similar results were obtained following stratification by age, race, smoking status, or body mass index. Conclusion: The greater likelihood of preeclampsia among sisters of women with a previous preeclamptic pregnancy is consistent with a pathophysiologic role for genetic and/or behavioral factors that cluster in families. The purpose of this study was to determine if women with preeclampsia are more likely to have a sister who also had preeclampsia. Study design: This was a population-based case-control study using data from Washington (WA) state birth certificates linked to hospital Cases were women with gestational hypertension (n = 1611) or preeclampsia (n = 1071); controls (n = 8041) had normotensive pregnancies. All women delivered their first child between 1987 and 2002 and had a sister with a previous delivery in WA. Results: Women with preeclampsia were 2.3 times (95% CI 1.8- 2.9) more likely to have a sister who had preeclampsia; those with gestational hypertension were 1.6 times (95% CI 1.3- 2.0) more likely to have a sister with gestational hypertension. Similar results were obtained in stratification by age, race, smoking status, or body mass index. Conclusion: The greater likelihood of preeclampsia among sisters of women with a previous preeclamptic pregnancy is con sistent with a pathophysiologic role for genetic and / or behavioral factors that cluster in families.