INTRODUCTION:This study examined survey data from before and after California expanded its Medicaid program under the Affordable Care Act. It assessed changes in the insurance status of smokers, the proportion of smokers in Medicaid, and the health and well-being of those smokers relative to their counterparts in other insurance groups. METHODS:The study compared two data sets from the California Health Interview Study, the 2011-2012 (N=42,935) and 2016 (N=21,055) surveys. Measures include health insurance status, smoking status, chronic health conditions, frequency of doctors' visits, and psychological distress. Data were analyzed in 2018. RESULTS:From 2011-2012 to 2016, the estimated number of California smokers in Medicaid nearly doubled from 738,113 to 1,447,945, and the proportion of smokers covered by Medicaid increased from 19.3% to 41.5%. Compared with those with private insurance, smokers in Medicaid were more likely to have chronic disease, have made five or more doctors' visits in the past year, and be in severe psychological distress. In 2016, a total of 51.4% of all adult smokers with chronic disease conditions and 57.8% of those in severe psychological distress were covered by Medicaid. CONCLUSIONS:With Medicaid covering a much higher proportion of smokers, especially of those smokers with chronic disease and in psychological distress, state Medicaid programs and plans must make tobacco cessation a top priority. They should encourage clinicians to ask, advise, and assist all smokers, track progress in reducing smoking prevalence, employ mass communication strategies to drive quit attempts, improve access to medications, and develop or expand programs to help smokers quit. SUPPLEMENT INFORMATION:This article is part of a supplement entitled Advancing Smoking Cessation in California's Medicaid Population, which is sponsored by the California Department of Public Health.