We have recently proposed a scoring system for risk assessment in primary myelodysplastic syndromes (MDS). In this score, one point is allocated to each of the following four parameters: bone marrow blasts > or = 5%, LDH > 200 U/l, hemoglobulin concentration < or = 9 g/dl, and platelet count < or = 100 x 10(9)/l. In a published series of 235 untreated patients with primary MDS, three prognostic groups (group A, score 0; group B, score 1 or 2; group C, score 3 or 4) were identified which differed significantly in both survival and rates of leukemic transformation. The present study was undertaken to reexamine the usefulness of our scoring system by applying it to an independent population of 263 newly diagnosed MDS patients. Morphological subtypes were RA in 53 (20%), RARS in 32 (12%), pure sideroblastic anemia (PSA) in 41 (16%), RAEB in 60 (23%), RAEB/T in 34 (13%), and CMML in 43 cases (16%). The predictive value of the Düsseldorf score could be assessed in 244 of 263 patients (initial LDH levels or platelet counts lacking in 19 cases). Forty-two patients were assigned to group A (low risk), 132 to group B (intermediate risk), and 70 to group C (high risk). Two-year cumulative survival was 86% in group A, 57% in group B and 14% in group C. Five-year cumulative survival was 53, 26 and 0%, respectively (p < 0.00005). Cumulative risk of AML 2 years after diagnosis was 3% in group A, 12% in group B, and 41% in group C (p < 0.05). Additional validation of the score was provided by extended follow-up of the initial patient population on which the scoring system was based. Survival curves in this patient population developed as predicted by the score. An important advantage of the Düsseldorf score is its ability to identify high-risk patients among the RA and RARS subgroups, even though by definition medullary blasts are less than 5%. The inclusion of LDH levels as a prognostic parameter also qualifies the Düsseldorf score for a correct assessment of CMML patients. In the new study population, LDH was confirmed as an important prognostic factor. After 2 years, actuarial survival for patients with LDH levels < or = 200 U/l was 61%, compared with 34% for patients with LDH > 200 U/l. Five-year cumulative survival was 32 and 14%, respectively (p < 0.00005).(ABSTRACT TRUNCATED AT 400 WORDS)