Fulminant hepatitis due to acute hepatitis C virus (HCV) infection is rarely observed. We present a case study of a 21-year-old male patient who developed HCV-associated fulminant hepatitis after receiving steroid pulse therapy for optic neuritis. Despite daily plasmapheresis, the disease progressed to irreversible liver failure with grade 3 hepatic encephalopathy by the 6th day after symptom onset. The patient received a liver transplant on the 8th day. Serum anti-HCV antibody was negative at that time, but became positive on the 12th day. Positive HCV RNA in the serum at admission was reported after transplantation. Positive changes in anti-HCV antibodies and acute hepatitis with massive necrosis in the histology of the explanted liver indicated fulminant hepatitis due to acute HCV infection. Because of severe hepatitis recurrence, he started 12 months of interferon therapy on the 48th day, and obtained sustained virological response. His anti-HCV antibodies became negative again by 1.5 years after cessation of therapy. HCV genomes recovered from the patient's serum on the 7th and 48th days revealed 2 different clones out of 20 clones with 30 % amino acid difference in hypervariable region 1 of HCV second envelope glycoprotein. One of the 2 clones expanded further after liver transplantation. We conclude that early diagnosis of HCV-associated fulminant hepatitis requires the detection of HCV RNA in the serum. Severe hepatitis recurrence after liver transplantation might occur in patients with fulminant hepatitis due to HCV because of its monoclonal expansion.