Objectives-Fentanyl, a synthetic opioid, has been increasingly identified in drug overdose deaths. This report describes trends in drug overdose deaths involving fentanyl by demographic characteristics and geographic regions from 2011 through 2016. Methods-Drug overdose deaths were identified from the National Vital Statistics System-Mortality (NVSS-M) multiple cause-of-death files (2011-2016) using International Classification of Diseases, 10th Revision underlying causes of death (codes X40-X44, X60-X64, X85, or Y10-Y14). NVSS-M records for drug overdose deaths were linked with literal text from death certificates. Drug overdose deaths involving fentanyl were identified using a methodology established collaboratively by the National Center for Health Statistics and U.S. Food and Drug Administration-referred to as the Drugs Mentioned with Involvement (DMI) methodology-supplemented with search terms identified using text analytics software. Fentanyl involvement was determined by the presence of any string term or phrase listing fentanyl, or any fentanyl metabolite, precursor, analog, or misspelling identified in the death certificate literal text fields (i.e., the causes of death from Part I, significant conditions contributing to death from Part II, and a description of how the injury occurred). Trends were evaluated using the National Cancer Institute's Joinpoint Regression Program. Results-The number of drug overdose deaths involving fentanyl was stable in 2011 (1,663) and 2012 (1,615), and began to increase in 2013, rising to 18,335 deaths in 2016. The ageadjusted rate increased from 0.5 per 100,000 standard population in 2011 to 5.9 per 100,000 in 2016, with the increase starting in 2013 (0.6 in 2013 to 1.3 in 2014 and 2.6 in 2015). Numbers and rates increased for all sex, age, and racial and ethnic subgroups, and most public health regions. Adjustment for improved drug reporting over the study period did not change the trend patterns observed.