Interferon therapy is indicated for the treatment of chronic hepatitis C and prevention of hepatocellular carcinoma. We describe the case of a 66-year-old Italian woman who received pegylated interferon alpha-2a plus ribavirin combined therapy for HCV-related chronic liver disease. Preliminary hematochemical, ultrasound and bioptic investigations did not show liver cirrhosis or hepatocarcinoma. After 24 weeks of treatment transaminase serum levels were in the normal range and circulating HCVRNA was undetectable by PCR qualitative assay. On week 46 a serious adverse event occurred, with rapid transaminase increase, severe hyperpyrexia, and abdominal pain, leading to interruption of interferon and ribavirin. Liver biopsy was repeated and it revealed poorly differentiated hepatocellular carcinoma. Only palliative care could be performed and the patient died of liver failure within 2 months. The present case underlines that hepatocellular carcinoma can be misdiagnosed in spite of laboratory and instrumental follow-up. More sensitive tools are needed for tumor detection, to avoid IFN impairment of the liver, even though it eradicates HCV.