Methods/ Results: We investigated 156 children with JMML registered in studies EWOG-MDS 98 or 2006 and tested for mutations in PTPN11, KRAS, NRAS, and CBL. Twenty-five children (16%) were clinically diagnosed as NF-1 based on >=6 café-au-lait spots (CALS) or family history plus CALS. The gene discussed is PTPN11; the disease is juvenile myelomonocytic leukemia.