The adverse consequences of passive smoking have spurred efforts to reduce environmental tobacco smoke (ETS) exposure among children, particularly in the home. For children with asthma, teaching them to avoid tobacco smoke at home is an important element of patient self-management. This strategy assumes that children can accurately assess household smoking behaviors and the level of their own exposure in the home. This study compared child and parental assessments of household smoking behaviors in an urban, low-income and largely ethnic minority sample of asthmatic children and their parents. While there was general parent-child agreement on the smoking status of household members, there was less agreement on duration of household smoking and the child's exposure to ETS. Objective validation measures (cotinine, nicotine) suggest that parents were better able than their children to assess hours of indoor smoking. Children's assessment of the extent of exposure to ETS may be problematic, with important implications for asthma patient self-management efforts.