Аннотация:The study of megacaryo-thrombocytic lineage was made in 88 patients with myelodysplastic syndrome (MDS). Normal platelet count was in 30, moderate thrombocytosis in 2, moderate thrombocytopenia in 35, deep one in 21 patients. Thrombocytopenic patients had high PDW and low MPV. Megacaryocytosis (51-200 megacaryocytes in the sample) was registered in 14 cases. In 37 cases the number of megacaryocytes ranged from 6 to 50, in 35 cases from 1 to 4 and in 2 cases no megacaryocytes were seen. 81 patients exhibited marked megacaryocytic dysplasia. Polyploid cells with disintegrated nuclei were encountered in 37%, 2-3 nuclear forms in 16% and one-nucleus microforms in 28% cases. Varying pathological types of megacaryocytes occurred in 31 patients. Patients with normal number of platelets and moderate thrombocytopenia had primarily pathological forms of megacaryocytes, in deep thrombocytopenia - very few megacaryocytes without dysplasia. The degree of thrombocytopenia and characteristics of dysplasia of megacaryocytes were unrelated to severity of both anemia seen in 92% patients and neutropenia seen in 62% patients. No cases of isolated cytopenia of the thrombocytic lineage was found. Number of platelets appeared prognostically important while morphological parameters were insignificant. In normal number of platelets median of survival was greater (p = 0.02) than in thrombocytopenia under 130×109/l (56.4 months and 14.6 months, respectively).