We report a case of non-sideroblastic refractory anaemia which evolved to a double lymphomyeloproliferative disorder. At presentation, bone marrow appearances and peripheral blood pancytopenia without myelomonocytosis were consistent with a diagnosis of non-sideroblastic refractory anaemia. Subsequently, the patient developed pronounced myelomonocytosis and lymphocytosis with prolymphocytes. Light and transmission electron microscopy as well as surface marker studies were compatible with a diagnosis of prolymphocytic transformation of chronic lymphocytic leukaemia/prolymphocytic leukaemia associated with myelomonocytic leukaemia. The pathogenesis of such double lympho-myeloproliferative disorders is discussed in the light of the evidence for common lymphoid and myeloid progenitor cells and some recent advances in the immunology of the myelodysplastic syndromes.