Legionella longbeachae is a very uncommon cause of community acquired pneumonia in Western countries. L. longbeachae does not grow on blood agar media and is usually not detected by sputum gram stain or blood culture. Furthermore Legionella urinary antigen testing fails to detect it. In this report we described a 79-year-old man with polymyalgia rheumatica under systemic corticosteroid treatment without other additional risk factors who developed a cultured-proven L. longbeachae community-acquired pneumonia complicated by an acute respiratory distress syndrome with septic shock. This case report demonstrates that non-pneumophila Legionella species must be taken into account as casual agents of community acquired pneumonia even in mild immunosuppressed patients, and empiric anti-Legionella antimicrobial coverage might be indicated until Legionella has definitively been rule out by adequate testing.