Exposure to secondhand smoke increases risk for infant illness and death. The objective of this study was to estimate the prevalence of complete smoke-free-home rules (smoking not allowed anywhere in the home) among women with infants in the United States.We analyzed 2004-2008 data from the Pregnancy Risk Assessment Monitoring System on 41,535 women who had recent live births in 5 states (Arkansas, Maine, New Jersey, Oregon, and Washington). We calculated the prevalence of complete smoke-free-home rules and partial or no rules by maternal smoking status, demographic characteristics, delivery year, and state of residence. We used adjusted prevalence ratios (APRs) to estimate associations between complete rules and partial or no rules and variables.During 2004-2008, the overall prevalence of complete rules was 94.6% (95% confidence interval [CI], 94.4-94.9), ranging from 85.4% (Arkansas) to 98.1% (Oregon). The prevalence of complete rules increased significantly in 3 states from 2004 to 2008. It was lowest among women who smoked during pregnancy and postpartum, women younger than 20 years, non-Hispanic black women, women with fewer than 12 years of education, women who had an annual household income of less than $10,000, unmarried women, and women enrolled in Medicaid during pregnancy.The prevalence of complete smoke-free-home rules among women with infants was high overall and increased in 3 of 5 states, signifying a public health success. Sustained and targeted efforts among groups of women who are least likely to have complete smoke-free-home rules are needed to protect infants from exposure to secondhand smoke.