We report a 20-year-old man with glycogen storage disease type Ia (GSD Ia) who presented multiple hepatocellular adenomas (HCAs) in 1993 and in whom percutaneous ethanol injection (PEI) was conducted as treatment for some enlarging tumors beneath the liver surface. In a 6-year follow-up period, we observed gradual enlargement of some of the HCAs, and the rapid growth of a newly developed tumor. In August 1996, one slow-growth HCA was 52 mm in diameter and was located beneath the surface of the liver. We conducted PEI therapy to prevent its spontaneous rupture. During the following year, another tumor developed beneath the liver surface, but showed extremely rapid growth, reaching 51 mm in diameter, from being undetectable, within 12 months. PEI therapy was again conducted for this newly developed tumor. Although additional PEI therapy was required for each tumor, because of suspected recurrence, no findings of discrete recurrence have been detected by computed tomography and magnetic resonance imaging for more than 2 years, up to the time of this study. We consider PEI to be a useful and effective therapeutic modality for individual HCAs in patients with GSD Ia.