To assess directly the effects of various risk factors on lung cancer incidence among never-smokers, large prospective studies are needed. In a cohort of 1.2 million UK women without prior cancer, half (634,039) reported that they had never smoked. Mean age at recruitment was 55 (SD5) years, and during 14 (SD3) years of follow-up, 0.2% (1469) of these never-smokers developed lung cancer. Cox regression was used to estimate relative risks (RRs) of lung cancer for 34 potential risk factors, of which 31 were non-significant (p>0.05). The remaining 3 risk factors were associated with a significantly increased incidence of lung cancer in never-smokers: non-white vs white ethnicity (RR=2.34, 95%CI 1.55-3.52, p<0.001), asthma requiring treatment vs not (RR=1.32, 1.10-1.58, p=0.003), and taller stature (height ≥165cm vs <160cm: RR=1.16, 1.03-1.32, p=0.02). There was little association with other socio-demographic, anthropometric or hormonal factors, or with dietary intakes of meat, fish, fruit, vegetables and fibre. The findings were not materially affected by restricting the analyses to adenocarcinomas, the most common histological type among never-smokers. This article is protected by copyright. All rights reserved.