Various kinds of second malignant neoplasms after successful treatment for childhood acute leukemia have been reported. The authors describe an unusual case of an olfactory neuroblastoma in a patient previously treated for childhood acute leukemia including autologous bone marrow transplantation. The prophylactic cranial irradiation and the total body irradiation during autologous bone marrow transplantation may have induced the development of their patient's olfactory neuroblastoma. Although a second primary olfactory neuroblastoma is rare, it should be added to the list of second malignant neoplasmsin the sinonasal region.