The retrospective evaluation of bone marrow biopsies of 569 patients with primary myelodysplastic syndrome--pMDS--revealed 256 refractory anemias--RA--, 52 refractory anemias with ringed sideroblasts--RARS--, 133 refractory anemias with excess of blasts--RAEB--, 52 refractory anemias with excess of blasts in transformation--RAEB-t--, and 53 chronic myelo-monocytic leukemias--CMMOL--according to FAB-criteria, 23 patients were not otherwise specified (myelodysplastic syndrome: not otherwise specified--MDS.NOS--). RARS-patients had the best prognosis (median survival 41.9 months, incidence of leukemia 3.8%), followed by RA-patients (26.5 months, 16.4%), MDS.NOS-patients (22.4 months, 21.7%), CMMOL-patients (12.5 months, 49.1%). RAEB- and RAEB-t-patients had the worst prognosis (median survival time 8.5 and 4.6 months, incidence of leukemia 42.1% and 57.7%, respectively). But the survival times showed a considerable range in each FAB-subgroup with 0-154 months in RA or 0-52 months in CMMOL. To forecast life expectancy more precisely, a scoring system was developed using nine histopathological parameters, among which the three most important ones were determined: quantity of myeloblasts, myelofibrosis and ALIP's. The scoring system allows a determination of three risk groups with significantly different survival times. It is valid also for patients without increase of myeloblasts (< 5% myeloblasts in the bone marrow) and identifies high-risk MDS patients in this group. By this proposed scoring system, a prognostic approval in primary MDS can be achieved applying histopathology without regarding further methods herewith presenting a system which could be considered independently from hematologic, cytological or laboratory data.