TheCHRNA3rs1051730 polymorphism has been associated to chronic obstructive pulmonary disease (COPD), lung cancer and nicotine dependence in case–control studies with high smoking exposure; however, its influence on lung function and COPD severity in the general population is largely unknown.We genotyped 57,657 adult individuals from the Copenhagen General Population Study, of whom 34,592 were ever-smokers. Information on spirometry, hospital admissions, smoking behaviour and use of nicotinic replacement therapy was recorded.In homozygous (11%), heterozygous (44%) and noncarrier (45%) ever-smokers, forced expiratory volume in 1 s (FEV1) was 94.1% predicted, 95.3% pred and 96.5% pred, forced vital capacity (FVC) was 97.1% pred, 97.5% pred and 98.3% pred, and FEV1/FVC was 0.770, 0.773 and 0.777, respectively (all p<0.001 for trend). Smoking interacted with genotype on FEV1% pred and FEV1/FVC (both p<0.001). When adjusted for cumulative tobacco consumption, these associations remained significant. In ever-smokers, odds ratios for COPD in homozygotesversusnoncarriers were 1.3 (95% CI 1.2–1.4) for Global Initiative for Chronic Obstructive Lung Disease (GOLD) stages I–IV, 1.4 (95% CI 1.2–1.6) for GOLD II–IV and 1.7 (95% CI 1.3–2.1) for GOLD III–IV. The corresponding value for lung cancer was 1.8 (95% CI 1.2–2.6). Genotype was also associated with daily and cumulative tobacco consumption and with use of nicotinic replacement therapy in former smokers.In ever-smokers, theCHRNA3rs1051730 genotype associated with reduced lung function and increased COPD severity.