In the present study we analyzed the prognostic significance of several clinical, hematological, and histological parameters recorded at diagnosis in a consecutive series of 72 patients with primary myelofibrosis (PMF). Univariate analysis showed that the most significant indicators of poor survival were the following: age greater than 60, splenomegaly, anemia (hemoglobin > 10 g/dl), leukopenia (WBC < 4 x 10(9)/l or leukocytosis > 14 x 10(9)/l), and any of these histological features: adipose tissue and megakaryocyte reduction, prominent osteoblastic rims along the trabecular bone, presence of peritrabecular megakaryocytes (Mk), absence of normal or giant Mk. The multivariate analysis showed that only the level of hemoglobin and the presence of both normal Mk and fever independently influenced the prognosis. These parameters were used to set up a prognostic scoring system, allowing a feasible prognosis to be made for each patient at the time of diagnosis and identifying those patients in urgent need of new therapeutic approaches.