Adult survivors of childhood Acute Lymphoblastic Leukemia (ALL) whose treatment included cranial irradiation (XRT) have reduced bone mineral density (BMD). Fifty three survivors of ALL (aged 6-17 yr, 22 male), who had completed their treatment without XRT, at least one year previously, and 187 (5-19 yr, 86 male) healthy controls were examined with dual energy x-ray absorptiometry of the total body (TB) and L1 to L4 vertebrae (LS) and peripheral quantitative computer tomography (pQCT) at the distal and mid-radial site. The TB and LS BMD did not differ between the ALL survivors and controls. Distal radial trabecular BMD (difference -0.080 mg/cm³; 95% confidence interval (CI) -0.139 to -0.020; P = 0.009) but not total BMD (difference -0.006 mg/cm³; CI -0.051 to 0.039; P = 0.80) was lower in ALL survivors compared with controls. At the mid-radial site both endosteal (11% larger; P = 0.0001) and periosteal (4% larger; P = 0.001) circumferences were greater and cortical thickness thinner by 6% (P = 0.006) in the ALL subjects leading to an increase in the axial moment of inertia in the ALL subjects (difference 13%; P = 0.008). In conclusion BMD except at the radius is normal in childhood survivors of ALL treated without XRT. At the mid-radial site, we speculate that ALL or its treatment resulted in endosteal bone loss, cortical bone thinning but the axial moment of inertia and hence strength was maintained, as a result of bone gain at the periosteal surface.