According to the Barker hypothesis, intrauterine growth restriction and premature delivery adversely affect cardiovascular health in adult life. The association of childhood hypertension as a cardiovascular risk factor and birth weight has been understudied. In a prospective cohort study, the authors evaluated the effect of birth weight, gestational age, maternal prepregnancy body mass index (BMI), and child BMI z score at the time of enrollment on the systolic and diastolic blood pressure (BP) z score in 3024 (1373 women) consecutive outpatient clinic patients aged 2.05 to 18.58 years. The latest National Health and Nutrition Examination Survey (NHANES III) was used to calculate the age-dependent z scores. The median z scores of BMI (+0.48, range -6.96-6.64), systolic BP (+0.41, range -4.50-6.73), and diastolic BP (+0.34, range -3.15-+6.73) were all significantly greater than the NHANES III reference population. Systolic BP z score did not correlate with birth weight or gestational age, but did correlate with maternal prepregnancy BMI (r=090, P<.0001) and BMI z score (r=209, P<.0001). Diastolic BP z score positively correlated with birth weight (0.037, P=044), gestational age (r=052, P=005), BMI z score(r=106, P<.0001), and maternal prepregnancy BMI (r=062, P=0007). In contrast to what would be expected from the Barker hypothesis, the authors found no negative correlation between BP z score and birth weight or gestational age. This study suggests that a high BMI, a big mom, and a high birth weight are more important risk factors for hypertension during childhood than low birth weight or gestational age. © 2010 Wiley Periodicals, Inc.