On the basis of four cases of oesophago-tracheal fistulae developing in ventilated patients, the authors describe the pathogenesis of these lesions, related to circulatory disturbances in the tracheal mucosa in contact with the balloon of the balloon of the tracheal tube. The spontaneous course is rapidly fatal and the results of surgical treatment remain disappointing. Prevention of these lesions is essential but difficult. It is based above all on the use of "large volume and low pressure" balloons, with periodic exsufflation. The diagnosis of these lesions must be make early and is base upon the development of tracheal dilatation, even minimal and seen radiologically by the appearance of the tube balloon. Such a finding should lead to endoscopic exploration of the tranchea and oesophagus, in order that treatment may be strated rapidly.