We report a case of nosocomial legionellosis in a 63 year-old man who was managed with neurosurgery under the diagnosis of subarachnoidal hemorrhage and complicated pneumonia in the intensive care unit. A legionella species was reported from sputum culture and direct immunofluorescent antibody test revealed L. pneumophila (serogroup 2). Our patient's pneumonia was cured with medical therapy including erythromycin and was the first case of microbiologically confirmed legionellosis in Korea.