The International Agency for Research on Cancer has declared smoking to be a risk factor for hepatocellular carcinoma (HCC). However, passive exposure to cigarette smoke and use of noncigarette tobacco products on the risk of HCC has not been examined. Therefore, we evaluated the independent effects of different types of smoking exposure along with multiple risk factors for HCC and determined whether the magnitude of smoking was modified by other risk factors in men and women. We conducted a case-control study at The University of Texas M. D. Anderson Cancer Center where 319 HCC patients and 1,061 healthy control subjects were personally interviewed for several HCC risk factors. Multivariate logistic regression analysis was performed to estimate the adjusted odds ratio (AOR) and 95% confidence interval (CI) for each potential risk factor. Use of smokeless tobacco (chewing tobacco and snuff), cigars, pipes and passive smoking exposure were not related to HCC among noncigarette smokers. However, regular cigarette smoking was associated with HCC in men: AOR, 1.9 (95% CI, 1.1-3.1). Heavy alcohol consumption was associated with HCC in women: AOR, 7.7 (95% CI, 2.3-25.1). Cigarette smoking interacted synergistically with chronic infection of hepatitis C virus in men: AOR, 136.3 (95% CI, 43.2-429.6) and with heavy alcohol consumption in women: AOR, 13.7 (95% CI, 3.2-57.9). We conclude that sex differences were observed in HCC relationship with cigarette smoking and alcohol consumption. Controlling for smoking exposure might be a prudent approach to the prevention of HCC, especially in patients with chronic viral hepatitis infections.