BACKGROUND: Passive smoking is a serious health risk in non-smokers. The strength of tobacco control policies of the EU countries vary. This study aimed to investigate the relationship between secondhand smoke exposure, as assessed by exhaled carbon monoxide (eCO), and the strength of national tobacco control policies, in non-smokers in the EU. METHODS: Data were provided from the EU campaign 'HELP: for a life without tobacco' during national events settled in the 27 EU countries in 2006-2007. Individual information on age, gender, and eCO was obtained from 58,919 self-reported non-smokers. The strength of national tobacco control policies was scored by the Tobacco Control Scale (TCS). The relationship between eCO and TCS score was investigated using ecological and multilevel approaches. RESULTS: Both analyses reported a significant linear decrease in eCO per unit increase in TCS score, with a smaller estimation resulting from the multilevel analysis (beta=-0.03 ppm, 95% CI -0.04 to -0.02 vs -0.05, -0.02 to -0.08). CONCLUSION: The present study confirms, in a large European non-smoker population, the relevance of strong antismoking policies in reducing exposure to passive smoking. The findings give further reason to encourage European countries to strengthen their tobacco control policies to protect non-smokers from secondhand smoke.