A case of hypoplasia of the left lung is described in a healthy girl of 14. The diagnosis can be made by bronchography and fluoroscopy in most cases, but films to demonstrate the spine and occasionally bronchoscopy can be helpful. Angiocardiography has a part to play in the diagnosis of associated cardiac abnormalities, but the results may be misleading when considering the pulmonary circulation. Contrary to the usual description, asymmetry of the chest does not appear to be uncommon in these cases, with or without associated congenital defects of the vertebrae or ribs.