Hairy bacilli of Legionella pneumophila is widely widespread in the aquatic environment. Epidemiology of the disease in Poland is not known. In any case of sick of severe pneumonia not responding to treatment (antibiotics beta-lactams) one should think about Legionella infection. Very important is the initial assessment of the risk of exposure to infection. Preferred test for the diagnosis of infection in all patients hospitalized with a diagnosis of severe pneumonia is the determination of Legionella antigen in urine. In the case of confirmation of Legionella infection is recommended to take antibiotics from the group of fluoroquinolones. In patients intolerant to this group the macrolides are applied.