A 43 year old male presented with a marked eosinophilia and associated systemic symptoms. A diagnosis of myelodysplasia was made on the basis of bone marrow morphology and karyotype. Over a 12 month period the disease transformed into acute lymphoblastic leukaemia, confirmed by flow cytometry, cytochemistry, and immunohistochemistry. Karyotyping was abnormal with 5q- and -7 which persisted from diagnosis through to blastic transformation. He died following initial induction chemotherapy. Eosinophilic myelodysplasia is an uncommon condition in haematological practice and no previous report of lymphoblastic transformation has been found.