OBJECTIVE:Cigarette smoking and smoking-related diseases disproportionately affect low-income populations. Health insurance coverage of smoking cessation treatments is increasingly used to encourage quitting. We assess the relationship between state Medicaid coverage of smoking cessation treatments and past-year quitting in adult Medicaid beneficiaries. DATA SOURCES:2009-2014 National Health Interview Survey (NHIS); 2008-2013 indicators of state Medicaid coverage of smoking cessation treatments. STUDY DESIGN:A triple-differencing specification based on differences in Medicaid cessation coverage policies across states as well as within-state differences between Medicaid beneficiaries and a counterfactual group of low-income adults not covered by Medicaid. DATA COLLECTION/EXTRACTION METHODS:Individual-level NHIS data with restricted geographical identifiers were merged with state-year Medicaid coverage indicators. PRINCIPAL FINDINGS:Combined coverage of both cessation counseling and medications in state Medicaid programs was associated with increased quitting, with an estimated mean increase in past-year quitting of 3.0 percentage points in covered Medicaid beneficiaries relative to persons without coverage. CONCLUSIONS:Combined coverage of both smoking cessation counseling and medication by state Medicaid programs could help reduce cigarette smoking among Medicaid beneficiaries.