Avascular necrosis of bone (AVNB) is reported in two children after allogeneic bone marrow transplantation. Preparation therapy for transplantation included cyclophosphamide and total body irradiation. Corticosteroids, cyclosporine A, and methotrexate were used for graft-versus-host-disease prophylaxis. The possible role of combination therapy in development of AVNB is discussed, but a direct relationship with single agents was not found. However, an early diagnosis is important to institute conservative treatment and prevent irreversible damage to affected joints. Magnetic resonance imaging was found to be more sensitive than plain radiography in early detection of AVNB.