OBJECTIVE: To evaluate whether adolescent obesity is associated with difficulties in becoming pregnant later in life. DESIGN: Cross-sectional analysis of baseline data from a longitudinal cohort. SETTING: Multiethnic, community-based observational study of U.S. women. PATIENT(S): Three thousand one hundred fifty-four midlife women. MAIN OUTCOME MEASURE(S): Lifetime nulliparity and lifetime nulligravidity. RESULT(S): Five hundred twenty-seven women (16.7%) women had never delivered a baby. Participants were categorized by self-reported high school body mass index (BMI): underweight (<18.5 kg/m(2)), normal (18.5-24.9 kg/m(2)), overweight (25-29.9 kg/m(2)), and obese (>30 kg/m(2)). The prevalence of lifetime nulliparity increased progressively across the high school BMI categories: 12.7%, 16.7%, 19.2%, and 30.9%, respectively. Multivariable logistic regression analysis confirmed that women who were obese adolescents had significantly higher odds of remaining childless compared with normal weight women (odds ratio [OR] 2.84; 95% confidence interval [CI], 1.59-5.10) after adjusting for adult BMI, history of nongestational amenorrhea, marital status, ethnicity, study site, and measures of socioeconomic status. Furthermore, adolescent obesity was associated with lifetime nulligravidity (OR = 3.93; 95% CI, 2.12-7.26). CONCLUSION(S): Adolescent obesity is associated with lifetime nulliparity and nulligravidity in midlife U.S. women.