Objective The social gradient in smoking contributes substantially to the health gap between the rich and poor. Passive smoking by children is associated with increased risk of more severe asthma, respiratory diseases and infections, middle ear disease and Sudden Infant Death Syndrome. This study examined trends in the social gradient of children's exposure to secondhand smoke in Australian households between 2001 and 2010.

Design Series of cross-sectional national household surveys.

Results Between 2001 and 2010, the proportion of Australian households containing a child aged under 15 years and a smoker declined by 22%. However, there was no change in the most disadvantaged households, with half of these households still containing at least one smoker in 2010. There was a social gradient in outdoor smoking in all survey years but the prevalence of outdoor-only smoking increased in all socioeconomic groups by around 50% between 2001 and 2010. The presence of a child aged 5 years or younger in the household increased the chances that smokers only smoked outdoors.

Conclusions Children's exposure to indoor smoking in households that contain a smoker is declining in all socioeconomic groups but the social class differentials in such exposure remain. The proportion of children who live with a smoker declined in all social groups except the most disadvantaged households, with half of these households still containing a smoker in 2010. More needs to be done to reduce secondhand smoke exposure of children in socially disadvantaged households.