RECENT OPPORTUNITIES to care for several patients with bilateral and bilocular empyemata have stimulated our interest in these complicated forms of thoracic empyema. In order to arrive at satisfactory conclusions regarding their incidence and treatment, we have reviewed the cases of empyema at the University of Michigan Hospital from January, 1925, until August, I938. During this period, 418 patients suffering with thoracic empyema due to pyogenic organisms occurring following respiratory infections, were admitted to the various services of the hospital. These cases do not include those with pure or secondarily infected tuberculous empyema, those in which empyema followed thoracic operations such as pulmonary lobectomy, those secondary to esophageal perforation, those following spontaneous perforation of a pulmonary abscess into the pleural cavity, or contamination of the pleura subsequent to surgical drainage of a pulmonary abscess, and those secondary to subdiaphragmatic abscess.Of the 418 patients, I87 were classified as having chronic empyema of from several weeks' to years' duration at the time of admission. Many of these patients had had surgical or medical care elsewhere; their management at the University Hospital ranged from simple dilatation of a contracted drainage track to an extensive Schede thoracoplasty. The operative mortality rate in this group was i.i6 per cent, only two patients having died while in the hospital.During the years covered by this study, several methods of treatment were employed in the care of the 23I patients having acute empyema. All have been based, however, upon the well-understood principles of avoiding the establishment of an open pneumothorax until the lung has become fixed by pleural adhesions and of instituting early dependent drainage. Thirty-one of these patients died, giving a mortality rate of 12.4 per cent. BILATERAL EMPYEMA In Table I are presented the 12 cases of bilateral empyema occurring during the period of the study, an incidence of 2.9 per cent. Of these, three (Cases 2, 6 and 12) may be classified as chronic, while nine were acute at the time of admission. Four patients did not receive treatment, empyema not