Secondary leukemia and myelodysplastic syndromes have been reported in patients following treatment for a wide range of neoplastic disorders. However second malignancies after chemotherapy and/or irradiation for osteosarcoma are unusual. PROCEDURE: We report the case of a 15-year-old girl who developed a myelodysplastic syndrome with evolution to acute nonlymphocytic leukemia after treatment for osteosarcoma. Therapy-related acute leukemia karyotype findings such as abnormalities of chromosomes 5, 7, and 17 were found in the cytogenetic analysis. Moreover, using denaturing gradient gel electrophoresis and DNA sequencing, we detected the presence of a double germline mutation in exon 7 of the TP53 gene. CONCLUSION: This observation supports the possibility of a causal relationship between germline TP53 mutations and the development of secondary leukemia and myelodysplasia