PURPOSE: The purpose of this study was to find out the incidence of and clinical risk factors for magnetic resonance imaging (MRI)-detected osteonecrosis (ON) in children treated for lymphoma or solid tumors. PATIENTS AND METHODS: The development of ON was studied in 32 childhood cancer patients who underwent MRI scanning of the lower extremities at the end of their treatment. The underlying malignancy was Wilms tumor in 8 patients, non-Hodgkin lymphoma (NHL) in 8, Hodgkin disease (HD) in 7, rhabdomyosarcoma in 6, and other occasional solid tumors in 3 patients. RESULTS: Six of the 32 patients (19%) had ON. The mean age of the patients with ON at diagnosis was 12.7 years compared with 5.8 years for the patients without ON (P