*JMML is generally an aggressive disease but milder forms and transient myeloproliferations occur: (1) Few cases with a KRAS or NRAS mutation show an indolent clinical course and long-term survival, which entity is called RAS-associated autoimmune leukoproliferative disorder (RALD), (2) infants with Noonan syndrome develop a transient JMML-like myeloproliferation in 2.5–10% of cases, which is almost invariably associated with a PTPN11 mutation, (3) JMML with a germline CBL mutation may show spontaneous regression. Here, PTPN11 is linked to juvenile myelomonocytic leukemia.