Background: Legionellae are aerobic, gram-negative, non-spore-forming bacteria. Over 56 distinct Legionella species are encompassing at least 70 serogroups, approximately half of which have been isolated from, or detected in clinical specimens, but all species are regarded as potential human pathogens. Aim of the study: To detect the prevalence of legionella among pneumonia patients in environmental water samples in Sohag University Hospital. Methods: This study was conducted on 100 newly diagnosed patients with pneumonia on environmental water samples taken from 10 water outlets over the period from December 2016 to December 2017 at Sohag University Hospital. The following were done to all subjects: full history taking, full clinical examination, urine culture on Buffered Charcoal Yeast Extract (BCYE) Legionella Urine Ag test (UAG) and water culture on BCYE. Results: They were 44 males (44%), 3 of them were positive for legionella culture and 56 females (56%), 2 of them were positive for legionella culture. Their age ranged from 26-85 years with mean value 58.04±11.51 years. Cases with Legionella showed a significantly higher prevalence of neurological manifestations; need more ICU admission and ventilatory support, more likely to be males and smokers, cardiac, having more chest pain or GIT manifestations, higher degrees of dyspnea. Conclusion: This study found that smokers, males, having CAP with an underlying COPD and non-productive cough, GIT and neurological manifestation should be considered for Legionella infection. Patients hospitalized for more than 10 days, who acquired HAP should be suspected for Legionella until prove otherwise.