A hepatic tumor was found in a 57-year-old man with glycogen storage disease type 1a (GSD1a) with a mutation in exon 5 of the glucose-6-phosphatase gene (G727T). Partial hepatectomy was performed, and the tumor was histologically diagnosed as moderately differentiated hepatocellular carcinoma (HCC). On contrast-enhanced ultrasonography, the tumor had a late phase defect. Abdominal imaging with other modalities was also performed. More studies are needed to clarify the differences in imaging findings between GSD1a-associated HCC and other tumors such as adenomas.