A 75-year-old female known to have a chronic myelomonocytic leukaemia and an acquired FXI deficiency (FXI level, 5%) related to a FXI inhibitor (38 Bethesda units) was admitted to the hospital for acute pneumonia associated with a bulky pleural effusion. A therapeutic puncture was found to be essential for the patient. But, such a procedure is a haemostatic challenge which requires adequate preparation. A first treatment composed of intravenous immunoglobulins and immunosuppressive therapy failed to eradicate the inhibitor and to restore a normal FXI level. In this context, steroids or FXI concentrates were not recommended. Thus, small doses of recombinant activated factor VII were used to achieve haemostasis. The procedure was successful, the tolerance was good and no adverse events occurred.