The case presents development of Legionella pneumonia in a patient with a concurrent heamotological disease and reflects a real-life medical situation when a patient with an infectious disease suffering from its complications, polipragmasia and self-treatment, comes to an infectionist. The article describes difficulties of diagnostics and ways of treatment as well as development of underlying and concomitant diseases. Many ways of transmission, a wide variety of clinical manifestations, complications and outcomes demand from doctors to remain alert for legionellosis and require a constant improvement of our knowledge of the disease. The aim of this article is to summarize information about Legionella, including diagnostics, clinical manifestations and treatment and to present a clinical case with a unique transmission of the pathogen. The article describes different clinical strategies for legionellosis control. © 2020, Dynasty Publishing House. All rights reserved.