A clinicopathological study was performed on 90 patients (39 males - 51 females, age 68 years) with primary (idiopathic) myelofibrosis - osteomyelosclerosis (OMF) in order to correlate laboratory and histomorphological parameters with each other and to calculate factors of prognostic impact on survival. In addition to multiple interactions between various laboratory features, there was a significant correlation between degree of medullary fibrosis and osteosclerotic changes with sizes of spleen and liver, level of LDH and duration of relevant prediagnostic symptoms. In trephine biopsies of the bone marrow, reduction of hematopoietic tissue was assessed by evaluating the amount of fat cells plus the degree of osteosclerotic lesions. This histological parameter did not reveal significant relationships with hepatosplenomegaly, duration of relevant symptoms or length of disease, but was correlated with the clinical findings of bone marrow failure. On univariate analysis, several clinical (age greater than 45 years, presence of relevant prediagnostic symptoms, hemoglobin level less than 9 g/dl, counts of myelo- and normoblasts, thrombocyte count less than 100 and greater than 700 x 10(9)/l, spleen size and LDH level) and histological features (reduction of hematopoiesis, counts for megakaryocytes and lymphoid nodules) were found to exert a predictive value on prognosis. However, on multivariate regression analysis only age remained significant. This result apparently reflects the numerous interactions between the various clinical as well as histological variables tested.