A 61-year-old woman who was a New York City hospital employee developed fatal inhalational anthrax, but with an unknown source of anthrax exposure. The patient presented with shortness of breath, malaise, and cough that had developed 3 days prior to admission. Within hours of presentation, she developed respiratory failure and septic shock and required mechanical ventilation and vasopressor therapy. Spiral contrast-enhanced computed tomography of the chest demonstrated large bilateral pleural effusions and hemorrhagic mediastinitis. Blood cultures, as well as DNA amplification by polymerase chain reaction of the blood, bronchial washings, and pleural fluid specimens, were positive for Bacillus anthracis. The clinical course was complicated by liver failure, renal failure, severe metabolic acidosis, disseminated intravascular coagulopathy, and cardiac tamponade, and the patient died on the fourth hospital day. The cause of death was inhalational anthrax. Despite epidemiologic investigation, including environmental samples from the patient's residence and workplace, no mechanism for anthrax exposure has been identified.