Although pleural effusion is not uncommon in legionellosis, the development of empyema and the demonstration of the organism in pleural fluid are exceptional. We report four patients with pleural empyema with isolation of Legionella pneumophila in the pleural fluid culture. The patients were three males and one female, with ages ranging from 36 and 83 years. All had left pleuritic pain, fever and pleural effusion. The appearance of pleural effusion was purulent in two cases and serofibrinous in the other two. Initially, the diagnosis was only suspected in one patient. The other three received inadequate treatment, until the result of the culture of the pleural fluid in BCYE-alpha medium was known. After giving erythromycin therapy at high doses, the outcome was favorable in the four patients. It is concluded that, in the absence of another diagnosis, the presence of L. pneumophila should be systematically investigated in the pleural fluid although the disease is not clinically suspected.