Juvenile myelomonocytic leukemia is a rare but deadly myeloproliferative disorder of early childhood that infrequently progresses to acute leukemia. The pathogenesis of this leukemia has been linked to deregulated signal transduction, resulting in growth factor hypersensitivity. Several other myeloproliferative disorders appear to share growth factor hypersensitivity as a common pathophysiological mechanism and thus this leukemia serves as an important model. New treatment modalities, such as retinoid therapy, are emerging for juvenile myelomonocytic leukemia. Further understanding of deregulated signal transduction should pave the way for even more rationally designed therapy for this leukemia and related disorders.