The incidence of bone lesions at diagnosis of childhood acute lymphoblastic leukemia (ALL) is relatively high. However, no cases of severe osteoporosis with multiple vertebral collapses secondary to treatment in children with ALL have been reported. We report the case of a 9-year-old-boy with B-ALL, with no bone lesions at the diagnosis that, following the 4th block of aggressive chemotherapy (protocol B-ALL BFM 86), presented severe back pain and functional impairment with diffuse osteoporosis and vertebral collapses. He was treated with calcitonin, vitamin D, calcium, physical therapy and orthopedic corset. Osteoporosis progressed slowly during the following 2 months of chemotherapy and the boy developed dorsal kyphosis. After discontinuing antiblastic treatment progressive clinical improvement was observed, with complete resolution of kyphosis in about 6 months. An almost complete bone recovery was seen on X-ray survey at 26-months follow-up.