Cryptogenic fibrosing alveolitis has been reported to be associated with an increased risk of lung cancer. However, it has recently become apparent that cigarette smoking may be a risk factor for cryptogenic fibrosing alveolitis as well as for lung cancer, and so may confound the association between these conditions. We have therefore estimated the independent increase in lung cancer incidence in patients with cryptogenic fibrosing alveolitis compared with the general population in a population-based cohort study involving 890 subjects with cryptogenic fibrosing alveolitis and 5,884 control subjects drawn from the United Kingdom General Practice Research Database. The incidence of lung cancer was markedly increased among patients with cryptogenic fibrosing alveolitis (rate ratio [RR] 7.31, 95% confidence interval [95% CI] 4.47 to 11.93, p < 0.001), and adjustment for previous smoking history had little effect on this odds ratio (adjusted RR: 8.25, 95% CI 4.70 to 11.48, p < 0.001). This increase in lung cancer incidence remained when the analysis was restricted to current smokers (RR 7.36, 95% CI 1.54 to 35.19, p = 0.012). This study provides clear evidence that the incidence of lung cancer is increased in patients with cryptogenic fibrosing alveolitis, and that this effect is independent of the effect of cigarette smoking. Hubbard R, Venn A, Lewis S, Britton J. Lung cancer and cryptogenic fibrosing alveolitis: a population-based cohort study.