In the present study the authors evaluated the status of spinal bone mineral density (BMD) using dual-energy X-ray absorptiometry in a group of 31 children with acute lymphoblastic leukemia, treated by ALL-BFM protocols without irradiation, at different phases of their treatment. These patients were studied (1) within 2 months of diagnosis (group 1, n = 17, median time postdiagnosis 17 days), (2) during chemotherapy (group 2, n = 16, median time on treatment 22 months), and (3) shortly after completion of therapy (group 3, n = 10, median time postchemotherapy 13 months). Twelve patients underwent serial measurements in either of the groups they entered (6 patients of group 1 and 6 patients of group 2). The mean cumulative prednisone dose was 0.8, 4.3, and 5 g/m2 in groups 1, 2, and 3, respectively. A gradual decline of BMD from group 1 through group 3 was observed. The mean value of age- and sex-specific BMD z-score was -0.74 (+/-0.32) in group 1, -1.59 (+/-0.24) in group 2, and -2.03 (+/-0.27) in group 3; there was a statistically significant difference between groups 1 and 3 (p = .022). A BMD z-score < -2 was found in 3 (17%), 4 (25%), and 5 (50%) patients of groups 1, 2, and 3, respectively. In conclusion, a high incidence of reduced bone mass was observed during and shortly after treatment. These findings could have significant consequences in long-term survivors.