Quantitative computed tomography was performed to determine bone mineral density (BMD) at initial presentation and following 6-months of therapy in children with acute lymphoblastic leukemia (ALL). Of 46 children enrolled, the complete set of observations was available in 32. The combined mean BMD of three lumbar vertebrae at diagnosis and during treatment were 167.1+/-27.4 and 148.8+/-31.4 mg/ cm3, respectively (P=0.001). Twenty six children (81.2%) had a decrease in BMD on treatment. The mean BMD for each of 3 vertebrae declined as well. The mean T-scores at diagnosis and during therapy were -0.15+/-0.9 and -0.86+/-1.0, respectively (P=0.001). Conventional radiographs revealed metaphyseal lucencies which were replaced with metaphyseal dense bands with therapy. To conclude, there was a significant reduction of BMD in children with ALL following 6- months of treatment.