Electronic cigarettes (e-cigarettes) are battery-powered devices that deliver a heated aerosol, which typically contains nicotine, flavorings, and other additives, to the user. The e-cigarette marketplace is rapidly evolving, but the long-term health effects of these products are not known. Carcinogens and toxins such as diacetyl, acetaldehyde, and other harmful chemicals have been documented in the aerosol from some e-cigarettes (1-3). On May 5, 2016, the Food and Drug Administration (FDA) finalized a rule extending its authority to all tobacco products, including e-cigarettes.* The prevalence of e-cigarette use among U.S. adults has increased in recent years, particularly among current and former conventional cigarette smokers (4); in 2014, 3.7% of all U.S. adults, including 15.9% of current cigarette smokers, and 22.0% of former cigarette smokers, used e-cigarettes every day or some days (5). The extent of current e-cigarette use among U.S. working adults has not been assessed. Therefore, CDC analyzed 2014 National Health Interview Survey (NHIS) data for adults aged ≥18 years who were working during the week before the interview, to provide national estimates of current e-cigarette use among U.S. working adults by industry and occupation. Among the estimated 146 million working adults, 3.8% (5.5 million) were current (every day or some days) e-cigarette users; the highest prevalences were among males, non-Hispanic whites, persons aged 18-24 years, persons with annual household income <$35,000, persons with no health insurance, cigarette smokers, other combustible tobacco users, and smokeless tobacco users. By industry and occupation, workers in the accommodation and food services industry and in the food preparation and serving-related occupations had the highest prevalence of current e-cigarette use. Higher prevalences of e-cigarette use among specific groups and the effect of e-cigarette use on patterns of conventional tobacco use underscore the importance of continued surveillance of e-cigarette use among U.S. working adults to inform public health policy, planning, and practice.