Objective: Juvenile Myelomonocytic Leukemia (JMML) is a disease from the spectrum of myelodysplastic/myeloproliferative diseases and it is also included in the category of malignant diseases presently classified in histiocytic diseases. Hemophagocy tic syndromes classified in histiocytic diseases are included into the diseases of variable biologic behavior. The association of myelomonocytic leukemia (JMML) with neurofibromatosis type 1 (NF 1) has been known. The objective of this contribution is to demonstrate, in the present case of a patient with JMML and NF 1, complicated by a simultaneous secondary hemophagocytic syndrome – VAHS or MAHS (Virus associated hemophagocytic syndrome, or Malignancy associated hemophagocytic syndrome), the problems in differential diagnosis as well as in the therapy of combinations of these two serious histiocytic diseases. The case and results: The disease became manifest in a two and three quarter year old boy with a clinical picture of a febrile state with bronchopneumonia and hepatosplenomegaly, icterus, the blood count with leukocytosis, thrombocytopenia and anemia, the differential blood could being characterized by a marked leukocytosis with marked monocytosis and the finding of younger developmental forms of granulocytes and blasts. The simultaneously present hypoproteinemia, hypofibrinogenemia and global coagulopathy, the presence of active virus infection (Herpes simples and Coxsackie B1) as well as multiplication of macrophages in bone marrow and the signs of hemophagocytosis resulted in the diagnosis of a simultaneous VAHS. In spite of the therapy aimed at influencing malignity as well as hemophagocytic syndrome the course of the disease was rapid and fatal. Conclusion: JMML without successful allogenic transplantation is fatal in almost 100% of cases. VAHS, if not therapeutically influenced, may also result in death of the patient. In the situation of a lacking donor and rapid course of the two simultaneous complications, the child could not be saved.

        Key words: juvenile myelomonocytic leukemia, neurofibromatosis type 1, secondary hemophagocytic syndrome – VAHS (Virus associated hemophagocytic syndrome)