The authors report a case of acute myelo-monocytic leukaemia occurring in a patient, 3 years after the beginning of a typical paroxysmal nocturnal haemoglobinuria (PNH). An intermediate phase characterized by worsening of the anaemia was observed, with disappearance of the in vitro haemolysis tests. The kinetic studies showed a replacement of the early peripheral haemolysis by a bone marrow insufficiency with intra-medullary cell death. A review of the five previous reported cases of this association show that PNH is generally a typical one, so that acute leukaemia must be considered as an unfrequent but possible complication of any PNH.