Recent evidence suggests that inflammatory pathways are important mediators of carcinogenesis. Asthma, allergic rhinitis and atopic dermatitis are clinical manifestations of a systemic atopic disorder, which is associated with airway hyper-responsiveness and inflammation. We examined the effect of a history of asthma/atopy among 132 lung cancer cases (of which 72% were adenocarcinomas) and 163 controls, all of whom were non-smoking Chinese women, in combination with a single nucleotide polymorphism (-634C/G) in the interleukin-6 (IL-6) gene which regulates secretion of a pro-inflammatory cytokine found to be predominant in lung tumour tissue. We observed a slight increase in risk of lung cancer [odds ratio, OR = 1.5, 95% confidence interval (95% CI) = 0.8-2.6] and of adenocarcinoma (OR = 1.6, 95% CI = 0.9-3.1) with asthma/atopy alone. There was no effect of the IL-6 CG/GG genotype on lung cancer risk on its own. Among individuals with both asthma/atopy and the IL-6 -634 G allele, however, risk was increased at least 3-fold (OR = 3.1, 95% CI = 1.2-8.3 for all cancers and OR = 4.2, 95% CI = 1.5-11.6 for adenocarcinomas) relative to individuals with no asthma/atopy and the CC genotype. On stratified analysis, a significant increase in risk with asthma/atopy was restricted to those with the at-risk genotype (Pint < 0.05). Our findings are consistent with the role of chronic inflammation as an aetiologic factor among non-smoking Asian women, and suggest that asthma/atopy is a risk marker for susceptibility to the development of lung cancer.