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We treated an extremely rare case of a mycotic aneurysm with infection of an artificial blood vessel by Saccharomyces cerevisiae, which was the first case in Japan. The patient was an 84-year-old woman. Five months before hospitalization, replacement of the ascending aorta was performed for a dissecting aneurysm of the ascending aorta. On regular follow-up examination, she had no symptoms, but accumulation of a liquid was detected around the artificial blood vessel on computed tomography (CT) imaging. She was immediately hospitalized. An emergency operation was performed because of the infected aneurysm, which accompanied infection of the artificial blood vessel. We could not detect any microorganisms in the blood or tissue culture, but we made a diagnosis of S. cerevisiae infection after performing broad-range polymerase chain reaction (PCR), followed by deoxyribonucleic acid (DNA) sequencing analysis. When an infected aneurysm is suspected after imaging analysis, such as CT, in a patient without fever or chest pain and with poor inflammatory reactions, an infected aneurysm caused by a fungus should be considered, even though blood or tissue culture results are negative. It is important to perform histopathological examination using Grocott silver stain and genetic testing (broad-range PCR and DNA sequencing analysis) of the tissue to identify the fungal infection. In the elderly, the number of cases of infection with S. cerevisiae may increase, and these cases may require more attention in the near future.