Results of sequential chromosome and cytologic studies in a patient with erythroleukemia (EL) by FAB criteria are described here. Major karyotype aberrations (MAKA) as well as normal karyotypes were detected at presentation, when the patient showed erythroid hyperplasia with moderate leftward shift of erythropoiesis and trilineage myelodysplasia, a picture suggestive of multilineage involvement. Following conventional induction therapy, the patient entered a myelodysplastic phase (MDS) with the features of refractory anemia with excess of blasts and subsequently relapsed with classical EL with maturation arrest of erythroblasts. Chromosome studies revealed a 46, XY karyotype in the MDS phase and only MAKA at leukemia relapse. These findings provide further evidence of a multistep cytogenetic and clinicopathological evolution of EL. Concomitant cytogenetic and morphologic studies in this patient seem to suggest the presence of chromosomally abnormal erythroblasts and confirm the existence of a association between MAKA and maturation arrest of erythroblasts.