We report an outbreak comprising 50 confirmed cases of Legionnaires' disease in Edinburgh, Scotland, June 2012. In addition, there were 49 suspected cases. Epidemiological evidence suggests that a common outdoor airborne exposure occurred over south-west Edinburgh. This probably emanated from cooling towers in the north-east of the affected area, although not yet clearly linked by scientific evidence. The co-ordinated public health, environmental and clinical response helped prevent ongoing exposure and mitigated associated mortality and morbidity.