Myeloproliferative syndromes (MPS) are clonal proliferation of hematopoietic progenitor cells characterized by proliferation of 1 or a few cell lines such as granulocytic, erythroid, megakaryocytic or mastocytic. These syndromes include: chronic myeloid leukemia, polycythemia vera, essential thrombocythemia, myelofibrosis, chronic eosinophilic leukemia/hypereosinophilic syndrome, chronic neutrophilic leukemia and systemic mastocytosis. Diagnosis of MPS is often difficult due to need of differential diagnosis with reactive proliferation caused by primarily non-hematological factors. Differentiation of individual MPS forms is also difficult because of overlapping of particular clinical or laboratory adnormalities. Discovery of specific molecular aberrations in the last few years facilitates diagnostic procedures. The discovered gene mutations or their fusions are associated with production of proteins possessing tyrosine kinase properties. These discoveries resulted in the successful introduction of the targeted therapy with tyrosine kinase inhibitors in the recent years.