Avascular necrosis (avn) is a complication of treatment for malignancies in children and adolescents. The authors present a two-center retrospective of experiences with avn in children treated for acute lymphoblastic leukaemia or non-Hodgkin lymphoma (8 from 191 patients with newly diagnosed disease in total of 19 sites). The median age at diagnosis was 16.6 years. Avn was observed in 4.1% of the group, higher among males than females (7/1), both during and after therapy. Early diagnosis of the process has enabled 7 patients to avoid surgical intervention. The increased incidence of avn, the multimodal character of symptoms, but unknown late consequences of avn showed that prospective studies of early recognition and proper therapy are needed.