To examine the influence of sexual maturation (SM) on blood pressure (BP) and body fatness during puberty among African-American children. Longitudinal data were collected from 283 African-American children aged 9–15 years over a 1.5-year period. Measured anthropometric measures included height, weight, skinfold thickness, waist circumference (WC), and systolic and diastolic BP (SBP/DBP) at baseline, 1-year, and 1.5-year follow-up were used. SM was assessed using self-reported Tanner stages (range 1–5) at baseline. Spearman correlation and regression analyses were conducted to test associations between study variables. Early maturing girls had higher BP and body mass index (BMI = weight (kg)/height (m)2) at follow-up than nonearly maturing girls (SBP: 117.4 vs. 111.7; DBP: 66.3 vs. 60.7; BMI: 27.7 vs. 23.5; all P < 0.05, respectively). Baseline Tanner stage was positively associated with follow-up SBP (r = 0.28), DBP (r = 0.37), BMI (r = 0.45), skinfold thickness (r = 0.37), and WC (r = 0.40) in girls, but not in boys. The influence of SM on BP independent of body size was tested via several different multiple linear regression models by adding measures of body size and their changes (height and BMI) between baseline and follow-up. Early maturing girls had higher SBP and DBP (β = 4.30, P < 0.05; β = 3.28, P < 0.05; respectively) and BMI (β = 1.69, P < 0.05) at 1.5-year follow-up than their counterparts. In boys, a marginally significant reverse association (β = −1.05 to −1.19) between SM stages and DBP was detected. SM affects BP and body fatness in girls, and should be considered in assessment of BP and obesity in adolescents. Am. J. Hum. Biol., 2009. © 2008 Wiley-Liss, Inc.