THE opportunity to deliver the Carman Lecture is not only an honor but a high privilege. Through it, this Society honors the memory of a great physician. We take just pride and satisfaction in the fact that he was also a great radiologist. We remember him not only for his remarkable skill and ability as a diagnostician and for his permanent contributions in the field of radiology, but for his clear ideals which kept his work and writings on the highest plane of scientific honesty. Especially do we remember him for his kindly, sympathetic understanding and helpfulness of younger men and of those whose opportunities were limited. Russell Carman will be remembered best, perhaps, as the years pass, for his practical contributions to radiological diagnosis. With this in mind I have chosen for this address a subject of outstanding practical importance, with the hope that I may be able to present it in such a way that you will find in it suggestions which will be helpful to you and your patients in your everyday practice of radiology. It is only within the past decade that the frequency and importance of bronchiectasis have become recognized. Until 1922, when Sicard and Forestier introduced a method by which the bronchial tree could be visualized, it was believed that bronchiectasis was a rare disease. It is now known that it is one of the most common of pulmonary diseases. Even yet, a considerable percentage of cases are wrongly diagnosed. Nearly every patient with well-marked symptoms of bronchiectasis, especially if he has had hemoptysis, will have, at one time or another, a diagnosis of tuberculosis. Many such patients have spent long or short periods in tuberculosis sanatoria even though the sputum is persistently negative for tubercle bacilli. It is true that bronchiectasis is sometimes an accompaniment of tuberculosis of the lungs but the type which is now known to be so common is non-tuberculous. Etiology and Pathologic History Before we discuss the diagnosis and treatment of the disease, it is important to review briefly our knowledge of its etiology and the pathologic changes produced by it. In the little over a century which has elapsed since Laënnec first described bronchiectasis, many causes have been assigned to the disease. It is now recognized, however, that the majority of cases are due primarily to infections. An inflammation of the bronchi precedes bronchial dilatation in nearly all cases. The disease often follows the acute infections, especially influenza, measles, and whooping cough. Infection of the paranasal sinuses has only recently been recognized as a very common accompaniment, if not a cause, of bronchiectasis. Obstruction to a bronchus by a foreign body, a newgrowth, or by pressure is often followed by bronchiectasis, but even in such cases it seems likely that infection in a poorly aërated or atelectatic area of lung is the really determining cause of the bronchial dilatation.