Clinico-epidemiological data show that the most severe forms of hepatitis C virus (HCV) associated liver disease occur in patients with multifactorial liver damage. We found that the prevalence of hepatitis B virus (HBV) markers in anti-HCV positive patients with cirrhosis complicated by hepatocellular carcinoma (HCC) is higher than in cirrhotics with comparable age and disease history, but without HCC. HBV can persist in integrated forms in HBsAg negative, anti-HBc positive individuals and we may speculate that in such patients concurrent liver pathogens, as HCV, could cause HCC more easily than in patients without previous exposure to HBV. Analysing the relations between age at HCC diagnosis and the different risk factors in consecutive HCC patients we found that patients with single hepatitis virus infections (HBsAg and/or anti-HCV positive) were of an older median age than patients with multiple hepatitis virus infections. We also studied patients with compensated cirrhosis and hepatitis virus infections. untreated or treated with interferon-alpha. The independent effect of treatment was analysed by matching groups with regard to all the other significant HCC risk factors. The overall relative HCC risk was three times higher (risk ratio 3.1) in untreated vs treated anti-HCV positive patients and more than six times higher (risk ratio 6.2) in untreated vs treated anti-HCV positive/anti-HBc negative patients. The difference between treated and untreated patients was not statistically significant in hepatitis B surface antigen carriers and in anti-HCV positive/anti-HBc positive patients. The evidence that HBV coinfection may worsen the course of liver cirrhosis in patients with chronic hepatitis C is intriguing, but it has important practical consequences. It warrants the identification of high risk patients with chronic hepatitis C who need to be treated as early as possible and patients who can still benefit from interferon-alpha therapy once cirrhosis has already been diagnosed.