The author reviewed the records of 31 patients with asporogenic anaerobic empyema mostly seen in the wards of Internal Medicine, Juntendo University Hospital during the 27 years between 1961 and 1988, and obtained the following results. 1. There were 25 males and 8 females with an average age of 57.8 and 51.0 y/o (range, 25 to 79 y/o), respectively males more than forty years old occupied 74.2 percent of all cases. 28 patients (90%) had underlying conditions. 2. The cases of mixed infections with anaerobes and aerobes were only 22.6%. 3. The isolated bacteria were microaerophilic streptococcus, Bacteroides spp., Peptostreptococcus spp., Fusobacterium spp. etc. in this order. 4. There were no relationships between anaerobic infections with or without aerobes and putrid odor of pleural effusion. 5. Bacteroides spp. were isolated most in the group with putrid pleural effusion, however, they were not isolated in the group without putrid pleural effusion at all. This fact suggests that there is an intimate relationship between putrid odor and Bacteroides spp. 6. There was no deceased case which pleural effusion had been drained sufficiently with open or closed drainage. It suggests that sufficient drainage is the most important in therapeutic procedures of asporogenic anaerobic empyema.