Legionella pneumophila is a thin, aerobic, Gram-negative, pathogenic bacillus and the leading cause of Legionnaires’ disease (LD) in human, especially those with high risk conditions including immune system disorders or chronic lung diseases. The mortality rate of LD has been reported to be 60% or higher in inappropriately treated cases. Investigating the prevalence of L. pneumophila and identifying contaminated sources in hospital settings are essential steps that should be taken to control the disease and evaluate the efficacy of interventional strategies. Currently, the culture method is considered as the “gold standard” for detection of L. pneumophila and  LD diagnosis. In this case report of severe LD in Iran, we studied a 60-year-old male patient with underlying chronic obstructive pulmonary disease (COPD). We also presented the clinical and pathophysiological features of LD as well as its diagnostic and therapeutic methods. The importance of early diagnosis of L. pneumophila infection in patients with COPD is also highlighted.