The main reason for these problems is a tracheo-oesophageal fistula, either recurrence of the T.O. fistula, either persistance of a fistula which has been neglected during surgery. It has been observed in 7 infants from 19 operated atresias with such problems. These functionnal troubles may be produced by different other anomalies: oesophageal stenosis and or dyskinesia often observed, gastro-oesophageal reflux, associated anomalies of the larynx or trachea; laryngeal paralysis, tracheomalacia, tracheal epithelium metaplasia, tracheal compression by abnormal vessel, neurological dysmaturity, loss of swallowing reflex after a long postoperative course. Radiography and endoscopy are fundamental and complementary investigations. Endoscopy, under general anesthesia, must be minute (with optics), explore oesophageal and laryngo-tracheo-bronchic tract, and use several tests to demonstrate permeability of the fistula when it has been located. A special technique is presented. Several points must be outlined: 1--classical symptoms of persistant fistula are not reliable in authors' experience; any recurrent respiratory and swallowing problem requires investigations; 2--endoscopy and radiographic study have to be repeated sometimes to prove fistula; 3--responsability of some anomalies must be always discussed, because of their possible association with a fistula; several fistulas may also exist.