Photon absorption measurements of forearm bone density in 196 insulin-dependent patients, age 6-26 years, were compared with findings in 124 controls. Expected density, gm Ca/cm2 bone width (M/W), was calculated from regressions of M/W on ulnar length for white and black male and female controls. There were no significant correlations between M/W differences from expected and serum Ca, Mg, P, or alkaline phosphatase levels, estimated physical activity level, insulin dosage, or the presence of joint contracture. White females averaged 8.2% (± 1 S.E.M.) loss of M/W, as against white male average loss of 4.7% ± 1 and black female loss of 2% ± 2 (p < 0.001); the black male population was too small for separate analysis. M/W loss > 10% was seen in 29% of white males, 19% of blacks, and 48% of white females (p < 0.02). When the groups were further divided into those with duration of diabetes ≤ five years and those with duration > five years, significant reduction in M/W average loss over time was seen with white females (10.6% ± 1.2 to 3.7% ± 1.5, p < 0.0001). Expression of this defect in bone mineralization is controlled by race and sex acting independently of each other.