This paper describes and analyses some aspects of an outbreak of Legionnaires' disease in Victoria, commencing in late October 1998. In all, 18 cases caused by Legionella pneumophila serogroup 1 were notified within 10 days making this the largest outbreak in Victoria reported to that date. All cases had epidemiological links to an industrial estate in a northern Melbourne suburb. Extensive environmental sampling revealed Legionella bacteria in five cooling towers. Molecular subtyping techniques were used to compare clinical and environmental isolates. Isolates from one tower had a pulsed-field gel electrophoresis pattern that was indistinguishable from clinical isolates from eight cases. Control of outbreaks caused by Legionella bacteria requires rapid, coordinated responses to linked cases of disease. The Legionella urinary antigen test facilitated a rapid public health response, and culture and molecular subtyping of clinical specimens assisted in developing epidemiological links. Commun Dis Intell 2000;24:199-202.