Juvenile myelomonocytic leukemia (JMML) is a clonal myeloproliferative/myelodysplastic disorder of young children. Allogeneic hematopoietic stem cell transplantation (HSCT) is the only curative therapy, and a recent report from the European working group on myelodysplastic syndrome in Childhood (EWOG-MDS) indicates an event-free survival (EFS) of 52% at 5 years after HSCT