Even if the overall survival of children with cancer is significantly improved over these decades, the cure rate of high-risk pediatric solid tumors such as neuroblastoma, Ewing's sarcoma family tumors or rhabdomiosarcoma remain challenging. Autologous hematopoietic stem cell transplantation (HSCT) allows chemotherapy dose intensification beyond marrow tolerance and has become a fundamental tool in the multimodal therapeutical approach of these patients. Anyway this procedure does not allow to these children an event-free survival approaching more than 50% at 5 years. New concepts of allogeneic HSCT and in particular HLA-mismatched HSCT for high risk solid tumors do not rely on escalation of chemotherapy intensity and tumor load reduction but rather on a graft-versus-tumor effect. We here report an experimental study design of HLA-mismatched HSCT for the treatment of pediatric solid tumors and the inherent preliminary results.