A 19-year-old Japanese woman had been diagnosed with diabetes at the age of 9 years. She had a strong family history of diabetes, and genetic screening showed she had maturity-onset diabetes of the young type 3 (MODY3). Ultrasonography of the liver and magnetic resonance imaging showed multiple nodules consistent with hepatocellular adenoma (HA). Biopsy of the liver tumors revealed hepatocyte nuclear factor (HNF) 1α-inactivated HA. HA is known as a MODY3-related disease due to mutations in HNF1α. We present the first report of HA associated with MODY3 in Japan.