A man in his 20s visited a local physician because of upper abdominal pain, and an abdominal ultrasonography revealed hepatic tumors. He was then referred to our hospital. The patient had no history of blood transfusion, tattoos, habitual alcohol consumption, or narcotic drug use. Physical examination revealed abdominal fullness. Biochemical tests were negative for hepatitis virus markers and autoantibodies. Liver enzyme levels were high;further, the levels of alpha-fetoprotein and protein induced by vitamin K absence or antagonist-II (PIVKA-II) were elevated. Chest and abdominal dynamic enhanced computed tomography and magnetic resonance imaging scans showed multiple lung tumors and multiple liver tumors. An arterial phase contrast-enhanced computer tomography image showed multiple nodular heterogeneous hyperattenuating masses with washout in the equilibrium phase. A huge mass in the right hepatic lobe had a large area of central necrosis. We suspected hepatocellular carcinoma or undifferentiated mesenchymal tumor. Liver biopsy showed moderately differentiated hepatocellular carcinoma without fibrosis in the background liver. This patient was diagnosed with hepatocellular carcinoma that developed in a normal liver. The patient was treated with molecular-targeted drugs. Tumor enhancement decreased;however, the tumor size remained unchanged. The patient lived for 9 months. A search using the retrieval terms “non-hepatitis B virus/non-hepatitis C virus”, “non-cirrhotic”, “young adult”, and “hepatocellular carcinoma” revealed 12 case reports in the Igaku Chuo Zasshi database. Many cases had multiple tumors that were large in size as well as had venous invasion, and surgeries were performed because liver functions were normal. The present case is noteworthy because hepatocellular carcinoma with a non-hepatitis B virus/non-hepatitis C virus and non-cirrhotic background in a young patient is rare.