A large number of children sustain fractures after relatively minor trauma and several investigators have associated these fractures to a deficient accumulation of bone during growth. This study was conducted to better characterize the skeletal phenotype associated with low-energy impact fractures of the forearm in girls. The densities of cancellous, cortical, and integral bone and the cross-sectional area were measured in the radius of 100 healthy white girls (aged 4-15 years) using computed tomography (CT); 50 girls had never fractured and 50 girls had sustained a forearm fracture within the previous month. Fractured and nonfractured groups were matched for age, height, weight, and Tanner stage of sexual development. Compared with controls, girls with fractures had, on average, 8% smaller cross-sectional area at the distal radius (1.82 +/- 0.50 cm2 vs. 1.97 +/- 0.42 cm2; p < 0.0001) but similar cancellous, integral, and cortical bone densities. Neither radial length nor the amount of fat or muscle at the midshaft of the radius differed between girls with and without fractures. Both study subjects and matched controls were overweight. Although mean height was at the 50th percentile, mean weight was at the 90th percentile for age-adjusted normal values. Girls who sustain forearm fractures after minor trauma have small cross-sectional dimensions of the radius and tend to be overweight. The smaller cross-sectional area confers a biomechanical disadvantage that, coupled with the greater body weight, increases the vulnerability to fracture after a fall.