An 85-year-old man patient was admitted to the hospital complaining of fever and bilateral leg pain with swelling and erythema. A laboratory investigation revealed leukocytopenia, thus suggesting sepsis. Gram negative rods were detected in the specimen from the affected skin and empiric antibacterial therapy was initiated. The following day, his symptoms worsened and Pseudomonas aeruginosa was isolated from the blood culture and the skin specimen. Magnetic resonance imaging (MRI) did not show the typical characteristics of necrotizing fasciitis. In spite of intensive medical treatment, the patient's condition became critical, and on day 10 after admission, he died of multiple organ failure. An autopsy revealed necrotizing fasciitis due to P. aeruginosa. This is a rare case and its clinical presentation was atypical. The clinical diagnosis of this infection may be difficult, and therefore such cases warrant the careful attention of physicians.