Radiographic findings are reviewed for 69 patients with bacteriologically proven anaerobic infections in the thorax. On the initial films, the disease was confined to the lung parenchyma in 50%, and to the pleura in 30% of patients. The other 20% had combined pleural and parenchymal disease. Over 50% of cases had lung necrosis on the initial films, and many patients who began with a noncavitary pneumonia developed necrosis during hospitalization despite antimicrobial therapy. Once necrosis developed, resolution was slow with an average closure of 65 days for lung abscesses. Parenthymal disease was usually confined to one anatomic site. This site was almost always in a basal or posterior part of the lungs. Pleural effusions tended to progress very rapidly and always proved to be empyemas. Many empyemas occurred without recognizable pneumonic disease. A few were nosocomial, occurring as a complication of surgery, penetrating chest wounds, or subphrenic abscesses. Many patients developed empyemas as a complication of parenchymal disease, frequently while on antimicrobial therapy. Almost all empyemas required surgical drainage with either a rib resection or decortication.