A 52-year-old male gardener, who traveled to Guam Island several days ago, was admitted to our hospital with fever, cough and dyspnea. His chest X-ray showed bilateral infiltration and he was severely hypoxic and hypotensive on admission. He died of multiple organ failure in spite of intensive treatment with mechanical ventilation antibiotics including erythromycin. Legionella longbeachae serotype 1 was isolated from his sputum and was regarded as the etiologic agent. Legionella longbeachae was not isolated from the same type of leaf mold that he used as potting soil. This is the first case of Legionella longbeachae pneumonia from whom the organism was isolated in Japan.