Previous studies suggested a link between the use of G-CSF and increased incidence of myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML) after immunosuppressive therapy (IST) for severe aplastic anemia (SAA). This European survey included 840 patients who received a first-line IST with (43%) or without (57%) G-CSF. The incidences of MDS/AML in patients who did or did not receive G-CSF were 10.9% and 5.8%, respectively. A significantly higher hazard (1.9) of MDS/AML was associated with use of G-CSF. Relapse of aplastic anemia was not associated with a worse outcome in patients who did not receive G-CSF as first therapy, whereas relapse was associated with a significantly worse outcome in those patients who received G-CSF. These results emphasize the necessity of the current European randomized trial comparing IST with or without G-CSF and to alert physicians that adding G-CSF to IST is currently not standard treatment for SAA.