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/m2), class I obesity (BMI = 30-34.9 kg/m2), class II obesity (BMI = 35-39.9 kg/m2), class III obesity (BMI = 40-49.9 kg/m2) or super-obesity (BMI ≥ 50 kg/m2). 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/m2) 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 (pre-eclampsia 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. © 2010 RCOG BJOG An International Journal of Obstetrics and Gynaecology.