['Marrow fibrosis (MF) has rarely been studied in myelodysplastic syndromes (MDS). There are no data on occurrence and significance of MF in the context of the World Health Organization (WHO) classification of disease. In total, 349 bone marrow biopsies from 200 patients with primary MDS were examined for MF and its prognostic relevance. MF correlated with multilineage dysplasia, more severe thrombopenia, higher probability of a clonal karyotype abnormality, and higher percentages of blasts in the peripheral blood (P<0.002). Its frequency varied markedly between different MDS types ranging from 0 (RARS) to 16% (RCMD, RAEB, P<0.007). Two patients with MF showed a Janus kinase-2 mutation (V617F). Patients with MF suffered from marrow failure significantly earlier with shortening of the survival time down to 0.5 (RAEB-1/-2), and 1-2 (RCMD, RA) years in median (P<0.00005). The prognostic relevance of MF was independent of the International Prognostic Scoring System and the classification of disease.'] Does marrow fibrosis predict early fatal marrow failure in patients with myelodysplastic syndromes?