The purpose of the present study is to determine the role of the anaerobic bacteria in the chronic paranasal sinusitis. We cultured both aerobically and anaerobically, 80 specimen of pus we obtained by antral puncture. Fourteen per cent of the specimen were sterile (11 cases); we found a pure aerobic growth in 51% (41 cases), a mixed aerobic-anaerobic growth in 25% (20 cases) and a pure anaerobic growth in 10% (8 cases). This means that anaerobic organismes were isolated in 35% (28 cases): in 22% (18 cases) the anaerobic bacteria can be considered as the only pathogenes. These results show the great importance of the anaerobic bacteria in chronic and subacute paranasal sinusitis. The anaerobes live as saprofytes on the entire body but they become pathogene in certain conditions such as a low oxidation-reduction potential and a reduced oxygen tension. These conditions are found in the chronically infected paranasal sinuses. Probably the anaerobes do not initiate a sinusitis (except in the sinusitis from dental origine) but the primary infection is superinfected by anaerobes; once they have found ideal growth conditions, it's very difficult to destroy them: despite of several antral washings, a surgical intervention is often the only way. The best antibiotics against anaerobic sinusitis are clindamycin and tetracycline in general administration, and lincomycin, thiamfenicol and tetracycline for local application.