Chronic obstructive pulmonary disease risk is lower in black and south Asian people than white people, when adjusting for age, sex, deprivation and smoking status. The role of smoking intensity was assessed for its contribution to ethnic differences in chronic obstructive pulmonary disease risk, a relationship not previously investigated. This cross-sectional study included routinely collected primary care data from four multi-ethnic London boroughs. Smoking intensity (estimated by cigarettes per day) was compared between ethnic groups. Chronic obstructive pulmonary disease risk was compared between ethnic groups using multiple logistic regression, controlling for age, sex, deprivation, asthma and both smoking status and smoking intensity, examined independently. In all, 1,000,388 adults were included. Smoking prevalence and intensity were significantly higher in the white British/Irish groups than other ethnic groups. Higher smoking intensity was associated with higher chronic obstructive pulmonary disease risk. Chronic obstructive pulmonary disease risk was significantly lower in all ethnic groups compared with white British/Irish after adjustment for either smoking status or smoking intensity, with lowest risk in black Africans (odds ratio 0.33; confidence interval 0.28-0.38). Ethnic differences in chronic obstructive pulmonary disease risk were not explained in this study by ethnic differences in smoking prevalence or smoking intensity. Other causes of ethnic differences in chronic obstructive pulmonary disease risk should be sought, including ethnic differences in smoking behaviour, environmental factors, repeated respiratory infections, immigrant status, metabolism and addictiveness of nicotine and differential susceptibility to the noxious effects of cigarette smoke.COPD: SMOKING INTENSITY NOT BEHIND ETHNIC DIFFERENCES IN DISEASE RISK: Lower smoking intensity among blacks and south Asians does not explain their lower risk for chronic obstructive pulmonary disease (COPD). A UK team led by Alexander Gilkes from Kings College London analysed primary care data from more than a million people living in four multi-ethnic boroughs of the British capital. The researchers found that smoking status and intensity (as measured by number of cigarettes smoked per day) were both significantly higher in white British or Irish groups than in other ethnic populations. Even after statistically adjusting for smoking status or smoking intensity, however, the researchers couldn't account for the fact that people of south Asian or African descent had much lower prevalence rates of COPD, a lung disease linked to smoking. The findings suggest that other explanations of ethnic differences are still needed.