A 57-year-old woman was admitted to our hospital with characteristic aging of the face and thin body. Before admission, she had been treated for diabetes mellitus type 2 and had undergone amputation of the right leg due to ischemic disease. Abdominal computed tomography revealed primary liver tumor. Biopsy of the liver mass revealed poorly differentiated adenocarcinoma, not hepatocellular carcinoma. Genetic sequencing indicated a homozygous mutation in the Werner syndrome gene (WRN) and she was diagnosed with Werner syndrome with primary liver tumor. She declined medications for the liver tumor and eventually died 6 months after diagnosis. Werner syndrome is a rare autosomal recessive disorder associated with premature aging, and most cases of Werner syndrome have been reported from Japan. The main causes of death with Werner syndrome are malignancy and atherosclerotic vascular disease. With respect to malignancy, non-epithelial tumors are more common in Werner syndrome patients than in the general population. Some cases also show complications of epithelial tumors, as in the present case. When a liver tumor of unknown etiology is accompanied by characteristic aging of the face, Werner syndrome should be suspected and a comprehensive search for other tumors and complications of metabolic disorders undertaken.