The authors report five pediatric patients with acute lymphoblastic leukemia (ALL) in whom symptomatic aseptic osteonecrosis developed on therapy. All patients had been on treatment with a modified BFM protocol and developed osteonecrosis in the maintenance phase of the protocol. The avascular necrosis was multifocal in all. The authors' data suggest that dexamethasone used in the reinduction phase of the protocol may be the responsible agent although no definite proof exists. Since only symptomatic patients are reported, the true frequency of this complication may be significantly higher.