The clinical features of tracheomalacia depend on the location, length, and severity of the weakness of the tracheal wall. There is firm evidence that tracheomalacia in association with tracheoesophageal fistula is due to malformation and deficiency in the tracheal wall, but in other types of tracheomalacia the evidence is less conclusive. A classification is proposed, based on the known histopathologic and endoscopic changes. Endoscopy is considered the most reliable diagnostic examination.