Objective To examine the association between obesity subtypes and risk of early and late pre-eclampsia.Design Population-based retrospective study.Setting State of Missouri maternally linked birth cohort files.Population All singleton live births in the state of Missouri from 1989 to 2005.Methods The body mass index (BMI) was used to classify women as normal weight (BMI = 18.5-24.9 kg/m 2 ), class I obesity (BMI = 30-34.9 kg/m 2 ), class II obesity (BMI = 35-39.9 kg/m 2 ), class III obesity (BMI = 40-49.9 kg/m 2 ) or super-obesity (BMI ‡ 50 kg/m 2 ). Adjusted odds ratios (OR) and 95% confidence intervals (CI) for the association between obesity and the risk of pre-eclampsia were obtained from logistic regression models with adjustment for intracluster correlation.Results The rate of pre-eclampsia increased with increasing BMI, with super-obese women having the highest incidence (13.4%).Compared with normal weight women, obese women (BMI ‡ 30 kg/m 2 ) had a higher risk for pre-eclampsia (OR = 2.59, 95% CI = 2.87-3.01). This risk remained approximately the same for late-onset pre-eclampsia (preeclampsia occurring at 34 weeks or more of gestation) and was slightly reduced for early-onset pre-eclampsia (pre-eclampsia occurring at 34 weeks or less of gestation). Within each BMI category, the risk of pre-eclampsia increased with the rate of weight gain. Compared with normal weight mothers with moderate weight gain, super-obese women with a high rate of weight gain had the greatest risk for pre-eclampsia (OR = 7.52, 95% CI = 2.70-21.0).Conclusion BMI and rate of weight gain are synergistic risk factors that amplify the burden of pre-eclampsia among super-obese women.