Atypical pneumonia which contributes to an important proportion of community acquired pneumonia and Legionella pneumophila is a noteworthy pathogen worldwide. Legionnaires' disease, the severe form of pneumonia is predominantly caused by Legionella pneumophila serogroup 1. This study was conducted to determine the presence of Legionella pneumophila as a pathogen and the associated risk factors among the patients admitted with atypical pneumonia to a tertiary care hospital in Sri Lanka.