Background: Aflatoxins and hepatitis B virus (HBV) infections are important risk factors of hepatocellular carcinoma (HCC). This study assesses the population-attributable risk of these two factors, both jointly and separately, with respect to HCC. Methods: A case-control study was conducted in Sudan between 1996 and1998. Among 114 cases and 198 controls the consumption of peanut butter (a major source of aflatoxins) and HBV infection were investigated, as were drinking and smoking habits. Results: A clear dose-response relation was observed between increasing peanut butter consumption and HCC in people without HBV infection. Age-adjusted odds ratios for peanut butter consumption, HBV infection, and for the combination of both factors were, respectively, 5.1 (95% confidence interval = 1.8-13.9), 32.2 (4.0-257), and 41.5 (11.2-155). In this study, about 80% of the HCC cases are attributable to either peanut butter consumption or HBV infection. Depending on assumptions in the data analysis, 27-60% of all cases can be attributed to aflatoxin exposure and 49-52% to HBV infection; of these figures, 7-34% reflect a shared responsibility of the two factors. Conclusions: Both reduction of aflatoxin contamination of foods and HBV vaccination may be useful public health strategies in HCC prevention in Sudan.