One of the hallmarks of myelodysplastic syndromes (MDS) is their prognostic heterogeneity which complicates decision making regarding treatment for individual patients. The French-American-British (FAB) classification provides significant prognostic information, but carries the disadvantage of arbitrary demarcation of subgroups and overemphasis of morphological findings. In addition, there is considerable variation in survival and risk of acute myeloblastic leukemia (AML) development even within defined FAB subgroups, particularly in patients with refractory anemia with ring sideroblasts (RARS) and chronic myelomonocytic leukemia (CMML). Over the last 2 decades, several research groups have tried to identify additional clinical, hematological, and cell biological parameters in order to more accurately predict the natural course of MDS. These investigations have clarified that the number and extent of peripheral blood cytopenias, the bone marrow blast count, and the cytogenetic pattern are the most powerful prognostic indicators in MDS. Recent efforts have been directed at constructing prognostic scoring systems. These scoring systems try to enhance the predictive power by combining several features of the disease, which have proved their independent prognostic weight on multivariate analysis. The International MDS Risk Analysis Workshop substantially advanced the prognostic categorization of MDS patients by proposing a new scoring system (International Prognosis Scoring System, IPSS) that can be successfully applied to risk assessment of newly diagnosed patients and will likely prove useful for the design and analysis of therapeutic trials in MDS.