Chromosome analyses of bone marrow and peripheral blood cells were performed in a total of 51 patients with myelodysplastic syndromes (MDS) simultaneously with histopathological examination of resin-embedded bone marrow biopsies. Diagnosis of MDS was established by histopathology according to the French-American-British (FAB) classification, and reassessed by haematological data and clinical course. Clonal karyotypic changes were found in 30 of the 51 patients (59%): in 15 of 19 (79%) patients with refractory anaemia, 7 of 11 (64%) with refractory anaemia and excess of blasts (RAEB), 6 of 10 (60%) with RAEB in transformation, and 2 of 11 (18%) with chronic myelomonocytic leukaemia. The following three features of the histopathology revealed positive correlations with karyotype abnormalities: all cases of myelofibrosis in MDS (7/51) were accompanied by chromosome aberrations, microforms of megakaryocytes with reduced nuclear lobulation were observed in 18 of 30 cases with karyotype changes, and hypocellularity of haematopoiesis was associated with aberrations of chromosome 7 in 2 of 4 cases. No positive correlations were revealed between abnormal karyotypes and the transformation to acute leukaemia. The survival times were significantly decreased in patients with complex (3 and more) karyotype changes, when compared with patients with single (1-2) chromosome aberrations or normal karyotype, independently of the FAB classification.