A patient with lymphoma presented with pneumonia. While receiving antibiotics, he developed a rapidly spreading cellulitis. The soft tissues were debrided in the operating room, and pathological examination showed fat necrosis and a fibrinopurulent exudate in the fibroadipose tissue; direct immunofluorescence of the debrided tissue revealed the presence of Legionella pneumophila. Culture of the specimen obtained during the operation yielded L. pneumophila. To our knowledge, this represents the first case report of cellulitis due to L. pneumophila.