Myelofibrosis with myeloid metaplasia is the rarest myeloproliferative syndrom. Diagnosis is often easy in classical form, characterised by splenomegaly, leukoerythroblastic blood reaction and tear-drop erythrocytes on blood count and myelofibrosis on bone marrow biopsy. Evolution is highly variable with a median overal survival of 40 to 60 months and numerous prognostic factors especially anemia. No treatment has been demonstrated to improve survival (apart from allogenic bone marrow transplant). The rarity and the complexity of the disease are the most important difficulties for the definition of standardized diagnostic, prognostic and therapeutic criteria.