Results of bone marrow transplantation (BMT) in patients with Fanconi's anaemia (FA) in transformation are very poor and only a few cases with favourable outcome have been reported. We present the follow-up of two FA-myelodysplastic syndrome (MDS) patients with monosomy 7 and complex karyotype implicating chromosome 1. Both relapsed with acute myeloid leukaemia (AML) following an allogeneic BMT from an HLA-identical brother. The patients showed clonal cytogenetic evolution coinciding with the leukaemic transformation. In one patient, fluorescence in situ hybridization using X and Y chromosome probes detected an increase of host cells before clinical relapse. Both patients received a successful second allogeneic BMT from the same donor using a more intensive treatment regimen and remain in clinical and cytogenetic remission more than 3 years later.