Objectives: Legionnaires' disease (LD), which is atypical pneumonia with a broad variety of clinical symptoms, can lead to death despite its low incidence. There are multiple risk factors for LD, yet little information is available concerning what kind of environmental factors are linked to higher risk of LD development. We have experienced a fatal case of LD, which occurred in a decontamination worker after the Fukushima nuclear disaster. Case: A 53-year-old Japanese male visited our hospital with symptoms of fever, vomiting, diarrhea, and altered mental status, but not with respiratory manifestations. He was engaged in decontamination work, which generally includes operations such as the removal of topsoil in mountainous areas and cleaning roads and roofs of residential buildings with high-pressure water. He was required to wear specific equipment to prevent radiation exposure, and lived in a workers' dormitory or shared house, thereby sharing spaces with other workers. Normal antibiotic therapy did not improve his symptoms following his diagnosis with pneumonia. A urinary antigen detection test was then conducted, leading to a diagnosis of LD. Despite the change of antibiotic to levofloxacin, multiple organ failure led to his death. Conclusion: Decontamination workers may be at a high risk for developing LD and living and working conditions among them are possible contributors.