A survey of development of our knowledge about Legionnaires' disease since its detection to the first epidemics in Yugoslavia, is given. The etiology, pathogenesis, epidemiology, clinic and therapy of legionellosis are summarized. It is pointed out that the detection of Legionnaires' disease and successful fight against legionella infections require a close cooperation of clinicians, microbiologists, epidemiologists and corresponding technical experts. Their active attitude toward this disease is the basis of its prevention.