Antibiotic treatment of pleuro-pulmonary infectious diseases with ordinary germs brought a notable decrease in the frequency of pleural empyema without preventing them completely. The authors report 31 cases observed over the last 10 years. The initial signs corresponded to the classical picture but were rapidly masked by antibiotic treatment; it resulted in delay in hospital admission of over one month for more than half of the cases, for diagnosis was overlooked for a long time. In 19 patients, the pleural liquid was aseptic probably because of the antibiotics and of the lack of identification of anaerobic germs. The authors insist on the practical modalities of a medical treatment by puncture-lavage which, when associated with general antibiotic treatment, cured patients in 22 cases. On the other hand, the existence of bronchopleural fistula entailed surgery.