Legionellosis (legionnaires´ or veterans´ disease) is a severe infection that occurs mainly in the elderly and the immune compromised. The causal organism is a water bacterium, Legionella pneumophila; the case fatility rate is about 15%. The Dutch public became fully aware of this disease by an epidemic in 1999 among visitors of a large flower exhibition in the North West of the country. The politicians have in the mean time dictated that legionellosis should be bridled, even if this will cost as much as 1 billion euro´s. The technical methods that will be employed will be confronted however with a population growing older and more and more vulnerable. Dental treatment can also be a source of contamination; but so far no Dutch cases have been attributed to dentistry.