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Objective: The goal of this study was to evaluate the impact of a 10-month after-school physical activity (PA) program on body composition and cardiovascular (CV) fitness in young black girls. Research Methods and Procedures: Subjects were 8-to 12-year-olds recruited from elementary schools. Body composition was measured using anthropometrics {waist circumference and BMI, DXA [percentage body fat (%BF)] and bone mineral density (BMD)}, and magnetic resonance imaging [visceral adipose tissue (VAT)]. CV fitness was measured using a graded treadmill test. The intervention consisted of 30 minutes homework/healthy snack time and 80 minutes PA (i.e., 25 minutes skills instruction, 35 minutes aerobic PA, and 20 minutes strengthening/stretching). Analyses were adjusted for age, baseline value of the dependent variable, and sexual maturation (pediatrician observation). Results: Mean attendance was 54%. Compared with the control group, the intervention group had a relative decrease in %BF (p Ͻ 0.0001), BMI (p Ͻ 0.01), and VAT (p Ͻ 0.01) and a relative increase in BMD (p Ͻ 0.0001) and CV fitness (p Ͻ 0.05). Higher attendance was associated with greater increases in BMD (p Ͻ 0.05) and greater decreases in %BF (p Ͻ 0.01) and BMI (p Ͻ 0.05). Higher heart rate during PA was associated with greater increases in BMD (p Ͻ 0.05) and greater decreases in %BF (p Ͻ 0.005). Discussion: An after-school PA program can lead to beneficial changes in body composition and CV fitness in young black girls. It is noteworthy that the control and intervention groups differed in change in VAT but not waist circumference. This suggests that changes in central adiposity can occur in response to PA, even in young children, but that waist circumference may not be a good indicator of central adiposity.