Eosinophilia of variable duration, and subsequent progression to granulocytic sarcoma and acute myeloid leukaemia, has been infrequently reported in the literature. We report a patient with eosinophilia and normal cytogenetics who, after 24 years, showed transformation to a granulocytic sarcoma of the brain. Haematological counts were normal but the marrow revealed the cytogenetic abnormality trisomy 8 in 25% of mitoses. Subsequently an AML-M2 developed, showing a complex karyotype including the trisomy 8 in all metaphases. FISH analysis combined with cytological examination identified the trisomy 8 in blasts, eosinophils and dysplastic granulocytes only. Thus progressive leukaemic transformation selectively involved the myeloid compartment.