111 adults with acute myeloid leukemia were classified according to the morphological, immunological and cytogenetic features of their leukemic cells. A comparison was made between the clinical parameters on prognosis of these subgroups. Hemoglobin was the only parameter among all six FAB-subgroups to show a statistical significant difference. Other differences found applied to a few subgroups only. Again, immunologically or cytogenetically characterized subgroups did not show significant differences in clinical parameters or prognosis. Patients with pseudodiploid or hyperdiploid karyotype had a lower remission rate than the remainder. However, a cluster analysis in which all three classifications together with the clinical parameters were considered was best able to characterize groups with different prognosis.