A sporadic case of Legionnaires' disease was linked to travel on a cruise ship. Investigation identified two further cases of Legionnaires' Disease and one case of non-pneumonic Legionella infection. An Incident Team confirmed the source to be the ship's water system and control measures were instituted that included pasteurisation, super chlorination and chlorine dioxide dosing. The Public Health Laboratory Service (PHLS) Communicable Disease Surveillance Centre (CDSC), through the European Surveillance Scheme for Travel Associated Legionnaires' Disease, identified three previous cases associated with the same ship's water system including one fatality. Lessons for the international surveillance and control of Legionnaires' disease on cruise ships are discussed.