On the basis of clinical experience with 80 patients at Denver General Hospital from 1979 through 1984, we devised a three-part classification of empyema. Class I empyema (n = 12) is pleural effusion with pH less than 7.2 and with no bacteria. Patients with this type of empyema were treated with short-duration chest tubes. Further treatment was required in two of 12. There were no deaths. Class II (n = 28) is classic uniloculate empyema. Patients with this category of empyema were treated with chest tubes, with two deaths. Class III (n = 40) is complicated empyema, with multiple loculations. Tube thoracostomy failed more often than not; decortication was required in 10 of 18 patients treated with prolonged tube drainage. Limited thoracotomy for drainage and placement of tubes was done in 22 patients. Five required extension of the thoracotomy and decortication. All 22 had resolution of the empyema with no additional procedures. Limited thoracotomy immediately or during the first week of treatment is recommended for all multiloculated or complex empyemas.