In 2011, about 21 percent of adults who smoke traditional cigarettes had used electronic cigarettes, also known as e-cigarettes, up from about 10 percent in 2010, according to a study released today by the Centers for Disease Control and Prevention. Overall, about six percent of all adults have tried e-cigarettes, with estimates nearly doubling from 2010. This study is the first to report changes in awareness and use of e-cigarettes between 2010 and 2011.