Legionnaires' disease (LD) is a severe form of community-acquired pneumonia (CAP) that often requires intensive care unit (ICU) admission and has a mortality rate ranging from 4% to 40%. Recent advances in diagnostic methods, such as urine antigen testing (UAT) and molecular testing, have improved the detection of LD. The incidence of LD has increased globally due to higher numbers of patients with risk factors, particularly immunosuppression, and improvements in diagnostic techniques. Pathogenesis involves high pulmonary Legionella DNA loads, impaired immune response, and changes in the lung microbiome. Clinical manifestations include severe lung injury, extrapulmonary symptoms, and non-specific laboratory findings. Treatment is primarily based on macrolides or quinolones, with prolonged therapy for severe cases. Factors influencing mortality include ICU admission, immune status, and nosocomial infection sources. Further research is needed to identify specific biomarkers of severity and to compare different treatment regimens.Legionnaires' disease (LD) is a severe form of community-acquired pneumonia (CAP) that often requires intensive care unit (ICU) admission and has a mortality rate ranging from 4% to 40%. Recent advances in diagnostic methods, such as urine antigen testing (UAT) and molecular testing, have improved the detection of LD. The incidence of LD has increased globally due to higher numbers of patients with risk factors, particularly immunosuppression, and improvements in diagnostic techniques. Pathogenesis involves high pulmonary Legionella DNA loads, impaired immune response, and changes in the lung microbiome. Clinical manifestations include severe lung injury, extrapulmonary symptoms, and non-specific laboratory findings. Treatment is primarily based on macrolides or quinolones, with prolonged therapy for severe cases. Factors influencing mortality include ICU admission, immune status, and nosocomial infection sources. Further research is needed to identify specific biomarkers of severity and to compare different treatment regimens.