Myelodysplasia and acute myeloid leukaemia (MDS/AML) developed in three cases of severe aplastic anaemia (SAA) and one case of congenital neutropenia (CN, Kostmann's disease) who received recombinant human granulocyte colony-stimulating factor (G-CSF) are reported. in these four MDS/AML cases, age at diagnosis of SAA/CN was 0-13 years, the cumulative dose of G-CSF was 98 mu g/kg to 10 mg/kg over 1-57 months, and the interval from initiation of G-CSF to MDS/AML was 25, 23, 31 and 57 months, respectively. These results suggest a link between SAA/CN and MDS/AML in relation to G-CSF administration; however, large studies are necessary to determine if such a risk is significant in patients with SAA/CN who are treated with G-CSF.