The Earned Income Tax Credit is the largest antipoverty program in the USA. In 1993, the Earned Income Tax Credit benefit levels were changed significantly based on the number of children in the family such that families with two or more children experienced an exogenous expansion in their incomes. Using data from the National Longitudinal Survey of Youth 1979 cohort, we use a triple-difference plus fixed effects framework to examine the effect of this change on the probability of smoking among low-educated mothers. We find that the probability of smoking for White low-educated mothers of two or more children significantly decreased relative to those with only one child, and this result is robust to various specification tests. This result provides new evidence on the protective effect of income on health through changes in a health-related behavior and therefore has important policy implications. Copyright © 2012 John Wiley & Sons, Ltd.