At present, the only recognised prognostic factor for primary high-grade osteosarcoma is the histological response to preoperative chemotherapy. Our study was designed to identify new diagnostic markers that could eventually have a prognostic value and therapeutic consequences. 80 patients under 20 years of age with primary osteosarcomas were studied while under treatment by the French Society of Paediatric Oncology OS 94 protocol. Paired normal and biopsy samples were collected. In addition, surgical resection specimens, following preoperative chemotherapy, were obtained in many cases. After genomic DNA extraction, an allelotyping analysis targeting microsatellites was planned. The studied DNA regions contained mainly Rb, p53, APC, p16, c-met, TWIST, c-kit, erbB2 and topoisomerases genes. The techniques used in this molecular analysis comprised mainly allelotyping study, quantitative real-time PCR, gene sequencing , immunohistochemistry. The first results showed the prognostic value of 7q31 region containing c-met and 5q21 containing APC (Br J Cancer, 2003, Entz-Werlé et al.), 7p21 containing TWIST (Int J Cancer, 2005, Entz-Werlé et al.) and 4q21 targeting c-kit gene (J Clin Oncol, 2005, Entz-Werlé et al.).