Wet cooling systems are often associated with large outbreaks of Legionnaires' disease. Several European countries have legislation for registering such systems. The authors aimed to obtain an overview of the situation in Europe. A questionnaire survey was sent to 35 of the countries that collaborate in the European Working Group for Legionella Infections. In two countries it was passed to a regional level (to three regions in both Belgium and the United Kingdom), so that 39 countries or regions were sent the survey; 37 responded. Nine countries stated having legislation for the registration of wet cooling systems. Separate legislation exists at a regional level for two regions in Belgium and all three regions in the UK, giving a total of twelve countries/regions with legislation. In nine of these countries/regions, the legislation has been introduced since 2001. All of these countries/regions require periodic microbiological monitoring between twice a year and weekly; in nine, the legislation requires periodic inspection of the systems. Regulations for the registration of wet cooling systems should be required by public health authorities. During an outbreak of legionellosis, a register of wet cooling systems can speed up the investigation process considerably. The authors believe that the European Centre for Disease Prevention and Control (ECDC) should take the initiative to propose European Community (EC) regulations for all Member States.