Objective Children are vulnerable to secondhand smoke (SHS) exposure because of limited control over their indoor environment. Homes remain the major place where children may be exposed to SHS. Our study examines the magnitude, patterns and determinants of SHS exposure in the home among children in 21 countries (19 low-income and middle-income countries and 2 high-income countries).

Methods Global Adult Tobacco Survey (GATS) data, a household survey of people 15 years of age or older. Data collected during 2009–2013 were analysed to estimate the proportion of children exposed to SHS in the home. GATS estimates and 2012 United Nations population projections for 2015 were also used to estimate the number of children exposed to SHS in the home.

Results The proportion of children younger than 15 years of age exposed to SHS in the home ranged from 4.5% (Panama) to 79.0% (Indonesia). Of the approximately one billion children younger than 15 years of age living in the 21 countries under study, an estimated 507.74 million were exposed to SHS in the home. China, India, Bangladesh, Indonesia and the Philippines accounted for almost 84.6% of the children exposed to SHS. The prevalence of SHS exposure was higher in countries with higher adult smoking rates and was also higher in rural areas than in urban areas, in most countries.

Conclusions A large number of children were exposed to SHS in the home. Encouraging of voluntary smoke-free rules in homes and cessation in adults has the potential to reduce SHS exposure among children and prevent SHS-related diseases and deaths.