Introduction: Legionella pneumophila can cause severe community acquired pneumonia which may be life threatening. This organism is found in aquatic environments and infection is acquired through inhalation of aerosols. Few studies conducted in Sri Lanka have confirmed the presence of this organism in cooling tower water in Sri Lanka. Published data regarding human cases of legionellosis in Sri Lanka is not available. Objective: To determine the prevalence of community acquired pneumonia due to L. pneumophila among patients who required hospital admission and assess the risk factors associated with this infection. Methods: The study was carried out from July 2014 to June 2015 at the Teaching Hospital, Peradeniya. Expectorated sputum or endotracheal secretions and urine specimen were collected within 24 hours of admission after obtaining consent from all adult patients admitted during the study period with community acquired pneumonia. Respiratory specimens, if obtained, were inoculated onto Buffered Charcoal Yeast Extract (BCYE) agar and were inoculated at 35 º C-37 º C for 7 days and observed for typical colonies. Urine specimens were stored at-20 º C and ELISA test was performed for the detection of L. pneumophila serogroup 1a antigen. Results: Eighty urine specimens and 27 respiratory specimens were obtained form 80 patients. None of the respiratory specimens grew suspected colonies of L. pneumophila and all urine specimens were negative for L. pneumophila serogroup 1a antigen. Conclusion: L. pneumophila serogroup 1a was not identified as the pathogen responsible for community acquired pneumonia in this study sample.