Tobacco smoking and alcohol drinking histories were obtained from 194 patients with hepatocellular carcinoma (HCC) and 456 hospital controls, and the results were analysed in conjunction with the results of serological determinations of hepatitis B surface antigen (HBsAg), antibody to HBsAg (anti-HBs) and antibody to hepatitis B core antigen (anti-HBc) in all subjects, as well as the presence or absence of cirrhosis in HCC patients. The relative risk (RR) of HCC (and 95% confidence interval) among HBsAg-positive subjects was 13.7 (8.0–23.5), whereas the excess risk among antibody-positive subjects was small and statistically non-significant. In the presence of cirrhosis the RR for HBsAg-positive subjects was considerably higher (30.7 vs. 7.1 among HBsAg-positive subjects without cirrhosis) indicating that HBV may affect the development of HCC through at least two different and potentially multiplicative mechanisms (DNA integration and liver regeneration). Moderate ethanol consumption does not affect the risk of HCC, but there is a statistically significant and dose-dependent association between tobacco smoking and HBsAg-negative HCC. In most of the developed countries of Europe and North America, where the prevalence of HBsAg carrier state is very low and tobacco smoking very common, more cases of HCC may be due to tobacco smoking than to HBV, even though the RR for HCC is much higher among HBsAg carriers than among tobacco smokers.