Purpose: To determine the joint effect of young maternal age and obesity status on the risk of preeclampsia and eclampsia among a large cohort of singleton pregnancies. Methods: Data were obtained from birth cohort files recorded in the state of Florida during the years 2004-2007. The study sample consisted of mothers aged 13-24 (n = 290,807), divided into four obesity categories on the basis of prepregnancy body mass index (BMI): nonobese (BMI < 30), Class I obese (30.0 ≤ BMI ≥ 34.9), Class II obese (35.0 ≤ BMI ≥ 39.9), and extreme obesity (BMI ≥ 40). Nonobese mothers (BMI < 30) between the ages of 20 and 24 years were the reference group. Logistic regression models were generated to adjust for the association between preeclampsia, obesity, and maternal age with sociodemographic variables and pregnancy complications as covariates. Results: The overall prevalence of preeclampsia in the study population was 5.0%. The risk of preeclampsia and eclampsia increased significantly with increasing BMI and decreasing age. Extremely obese teenagers were almost four times as likely to develop preeclampsia and eclampsia compared with nonobese women aged 20-24 years (adjusted odds ratio [95% confidence interval] = 3.79 [3.15-4.55]). Whereas obesity elevated the risk for preeclampsia and eclampsia among all women in the study, teenagers were most at risk because of the combined effects of young age and obesity. Conclusion: Effective obesity prevention strategies should continue to be advocated for all teenagers, in addition to innovative approaches to teenage pregnancy prevention. © 2010 Society for Adolescent Medicine.