Background: CYP2C9 enzymes are important in the metabolism of procarcinogenic chemicals such as polycyclic aromatic hydrocarbons (PAHs) found in tobacco smoke. Two functional variants in the CYP2C9 gene (CYP2C9*2 and CYP2C9*3) are known to be associated with decreased enzyme activity towards tolbutamide and warfarin, while this has not been investigated for PAHs. We hypothesised that these two variants in the CYP2C9 gene influence risk of tobacco-related cancer. Methods: In a prospective study of the general population (n = 10 392) with 60 years of follow-up, the Copenhagen City Heart Study, we associated two variants of CYP2C9 (CYP2C9*2 and CYP2C9*3) with risk of tobacco-related cancer and all cancer. All results were re-tested in a cross-sectional study of the general population (n = 36 856), the Copenhagen General Population Study. Results: We found no association between any of the CYP2C9 genotypes and risk of tobacco-related cancer, individual tobacco-related cancers, or all cancer. For the combined carriers (any CYP2C9*2 or CYP2C9*3 heterozygotes or homozygotes) vs. non-carriers we had 90% statistical power to exclude measures of relative risks below/above 0.8/1.2 and 0.9/1.1 in the Copenhagen City Heart Study and below/above 0.8/1.3 and 0.9/1.1 in the Copenhagen General Population Study for tobacco-related cancer and all cancer, respectively. Conclusion: Genetic variations in CYP2C9 do not affect risk of tobacco-related cancers. (C) 2010 Elsevier Ltd. All rights reserved