Fanconi anaemia (FA) is a rare recessive DNA repair disorder clinically characterised by congenital malformations, progressive bone marrow failure and a high propensity for developing malignancies at an early age, predominantly acute myeloid leukaemia (AML) and squamous cell carcinoma. It is conceivable that a number of patients with hypomorphic mutations are not diagnosed as FA until severe complications in the treatment of a malignancy occur. Here, we report on a patient with FA-A, diagnosed only at the age of 49 years due to persistent pancytopenia and myelodysplastic syndrome/AML induced by a first cycle of chemotherapy for bilateral metachronic breast cancer. This exceptional case clearly demonstrates that, in instances of long-lasting mild pancytopenia or development of malignancies, especially at an unusually young age, FA should be ruled out, irrespective of the patient's age and features, especially before inflicting severe genotoxic stress.