Legionnaires' disease (LD) is a severe form of pneumonia which is caused by bacteria of the genus Legionella. They are widespread in fresh water and can also colonize technical water systems where they might present an infection risk. Since 2001, notification of laboratory-confirmed LD is mandatory in Germany. From 2001-2009, a total of 3672 cases of LD were registered. During the first 7 years, case numbers increased (2001: 127; 2007: 536 cases) but have remained stable during the past 2 years (2008: 525; 2009: 503 cases). In 2009, 49.6% of cases were attributed to an infection in the community, 33.2% were travel associated, and 13.6% were nosocomial. The average case fatality rate between 2001 and 2009 was 6.5%. However, the case fatality rate of nosocomial cases was three times as high compared to cases with non-nosocomial exposure. The network for community-acquired Legionnaires' disease (CAPNETZ) estimates that there are 20,000 cases per year in Germany. Thus, the number of reported cases represents only a small proportion of the actually occurring cases. It is likely that specific LD-diagnostics are insufficiently used. Hence, physicians should test more patients with pneumonia for LD. In particular, because of the high case fatality, nosocomial pneumonia cases need to be tested; identified LD cases require rigorous investigational and corrective action. In order to obtain evidence-based data on the relationship of water contamination and the risk for LD, it would be desirable, if (in addition to the patients' epidemiological data) the results of water texts relating to a given case were also reported systematically.