We report the case of a woman splenectomized to treat her hairy cell leukemia (at the moment in remission) 11 years before the detection of neutropenia. The neutropenia began just after the treatment of pulmonary embolism by acenocoumarol. The neutropenia disappeared quickly after substitution of acenocoumarol by fluindione. We discuss the attribution of the neutropenia to acenocoumarol and the part played by hairy cell leukemia.