An aberrant right upper lobe (RUL) bronchus arising from the trachea (tracheal bronchus) can be responsible for recurrent pneumonia. In this hospital, 2% of children requiring bronchoscopy for respiratory symptoms are found to have a tracheal bronchus, which is frequently thought to be an incidental finding. We reviewed findings in 18 patients to determine when a tracheal bronchus is of clinical significance. The age at presentation ranged from 1 day to 54 months (mean 17 months). The children had recurrent pneumonia (nine), stridor (six), respiratory distress (two) and a thoracic mass (one). Other congenital abnormalities were present in 14, including Down syndrome (two), tracheoesophageal fistula (two), and fused or hypoplastic first and second ribs (four). Recurrent RUL pneumonia was present in five. Bronchiectasis or bronchial stenosis was shown by bronchography in four of five; in all five the right upper lobe was surgically resected, with resolution of the recurrent pneumonias. The presence of a clinically significant tracheal bronchus should be considered in every child with recurrent RUL pneumonia, especially in children with Down syndrome or rib abnormalities; if bronchiectasis or bronchial stenosis is found, surgical resection should be performed.