Clinical, haematological, cytogenetic features and therapeutic problems of 51 patients with MDS were examined. Patients were distributed in 5 FAB subgroups: RA 21, SA 7, RAEB 8, RAEB-t 9 and MMCL 6 patients. Leukaemic transformation occurred in 3 RA, 3 RAEB, 7 RAEB-t and 3 MMCL patients. No SA patient suffered from leukaemic transformation. Cytogenetic alterations occurred in 13 of 29 examined patients; 5q- was the most common abnormality. We did not find any relation between chromosomal anomalies and FAB subgroups. Leukaemic transformation, however, was more frequent in patients with cytogenetic aberrations. In some cases it was not easy to determine the precise diagnostic allocation according to FAB subgroups; it is possible, however, to subdivide MDS prognosis into 2 classes. The more satisfactory therapy of leukaemic transformation is often due to low doses of Ara-C; this therapy allowed a better survival and sometimes to obtain CR which in a M6 ANLL patient continued for 24 months.