The annual global incidence of legionellosis is reported between 4–20 cases per million population. Legionellosis presents two, distinct clinical entities: multisystemic Legionnaires’ disease, with severe pneumonia, and Pontiac fever, a self-limited flu-like illness. Additionally, many those who seroconvert to Legionella remain entirely asymptomatic. Although healthy individuals can contract Legionnaires’ disease, most often patients are elderly or debilitated or immunocompromised. The causative agent, Legionella pneumophila is Gram-negative, small aerobic coccoid rod, obligate or facultative intracellular. Water is the major environmental reservoir for legionellae; they can infect and multiply within amoebae and ciliated protozoa which are found in natural and manufactured water systems. Legionellae infect human macrophages and monocytes and they multiply within alveolar macrophages. Laboratory diagnosis of legionellosis is based on bacteriological, serological and molecular methods. Among them urinary antigen test, UAT, is widely used. In this article, we present the current situation of legionellosis, with the focus on consequences, recognition and treatment of the disease.