After decades of declining US smoking rates overall, most remaining smokers have low income, no college education, no health insurance or a disability. About 15 percent of US adults -- more than 36 million -- continue to smoke cigarettes. Half to three-fourths of them have one or more low-socioeconomic disadvantages, and the lowest socioeconomic categories have the highest smoking rates. The study concludes that continuing tobacco use is now concentrated among the least advantaged portion of society.