Water samples taken from hot water springs, from the water distribution system and from various places of consumption of thermal water were collected in an Austrian spa. 56.5% of the samples contained Legionella; serogroups 1, 3 and 5 of Legionella pneumophila were most frequently identified. The large number of positive Legionella samples indicates a potential risk of infection to patients, especially those undergoing inhalation treatment with thermal water, or those using a whirlpool or taking a shower. In those inhalators actually in use, no Legionella could be detected. Thus they are no source of infection when they are maintained and serviced properly. Thermal disinfection and service checks at regular intervals are suggested for the contaminated systems.