This study determines: (1) patterns of change from childhood to young adulthood in body mass index (BMI), systolic blood pressure (SBP), and diastolic blood pressure (DBP), (2) effects of elevated BMI values on changes in blood pressures (BP), (3) extent of tracking for SBP, DBP, and BMI, and (4) prediction of future risk for elevated BP from earlier values. Annual serial BP and BMI data were available for 198 white females, ages 8-22 years, enrolled in the Fels Longitudinal Study. Patterns of change in BMI were described by a random effects model with a time series model for the correlated residuals. Serial BMI measures were differentiated from age-specific means to measure relative individual BMI levels. Serial BP were analyzed using a similar model to the BMI where relative individual BMI levels were included as an explanatory variable. There was a general increasing trend for SBP, DBP, and BMI from 8-22 years, but the rates of increase declined with age. At the same chronological age, early menarche females had a significantly greater BMI mean value than late menarche females. An average increase of 1 kg/m2 in deviation from BMI population means resulted in an average increase of 1.2 mmHg in SBP and 0.6 mmHg in DBP. Having SBP and DBP levels 1 standard deviation above mean levels, relative to females at mean levels, as early as age 9 represents an odds ratio of 2 for exceeding national 75th percentile levels of SBP and DBP at age 21. Am. J. Hum. Biol. 10: 589-598, 1998. © 1998 Wiley-Liss, Inc.