Background Smoke-free policies (SFPs) in public places are increasing globally, but developing countries are lagging behind. Understanding youth attitudes towards SFPs can inform SFP initiatives.

Methods A multilevel logistic regression analysis of data collected from youth aged 13–15 years (2000–2006) who completed the Global Youth Tobacco Survey (GYTS) in 115 countries, primarily in the developing world, was conducted. The analysis examined relationships between support for SFPs and individual-level measures related to smoking status, and exposure to secondhand smoke (SHS), controlling for demographic and environmental factors of interest and country-level policy factors.

Results In all, 77.3% of 356 395 youth in 115 countries favoured SFPs, including majorities of non-smokers (78.7%) and smokers (63.6%). In the multivariable analysis knowledge of smoke harm was the strongest predictor of favouring SFPs (OR 2.42, 95% CI 2.27 to 2.67). Exposure to countermarketing (OR 1.40, 95% CI 1.25 to 1.57) and school anti-smoking education (OR 1.22, 95% CI 1.13 to 1.31) were also positively associated. Current smoking (OR 0.48, 95% CI 0.41 to 0.53), susceptibility to smoking (OR 0.46, 95% CI 0.40 to 0.52) and exposure to tobacco promotion were negatively associated. Significant country-level variation was observed. The presence of any national smoke-free legislation in a country was positively associated with youth favouring such policies.

Conclusions The majority of youth worldwide support, yet lack, smoke-free policies in public places, while being regularly exposed to SHS. Youth support of SFPs is most positively associated with knowledge of the harmful effects of tobacco smoke. Redoubling education efforts represents an opportunity to establish smoke-free environments and improve health of children in developing countries.