In 2005, the Advisory Committee on Immunization Practices (ACIP) recommended that the newly licensed tetanus, diphtheria, and acellular pertussis (Tdap) vaccine replace a single decennial dose of tetanus diphtheria (Td) vaccine for persons aged 10-64 years. According to these recommendations, Tdap may be used to protect against pertussis even when <10 years have passed since the most recent tetanus vaccination. For adults with infant contact and health-care personnel (HCP) with direct patient contact (two groups at increased risk for transmitting pertussis to those who are most susceptible), the single recommended Tdap dose is suggested to be administered as soon as 2 years after the last tetanus vaccination. To assess changes in tetanus vaccination coverage and the use of Tdap among U.S. adults, CDC analyzed data from the National Health Interview Survey (NHIS) for 1999 and 2008. This report summarizes the results of that analysis, which indicated that self-reported tetanus vaccination coverage (vaccination within the preceding 10 years) was 60.4% in 1999 and 61.6% in 2008. Among adults aged 18-64 years, Tdap coverage was estimated to be 5.9% in 2008. Of those who reported receiving a tetanus vaccination during 2005-2008, 52.0% reported receiving Tdap. Tdap vaccination coverage among adults with infant contact was 5.0% and among HCP was 15.9%. Of those adults with infant contact and HCP who had received a tetanus vaccination during 2005-2008, 60.0% and 60.3% reported receiving Tdap, respectively. Health-care providers should recommend Tdap vaccination to adults aged 18-64 years whose most recent tetanus vaccination was ≥10 years prior; the interval for HCP and persons with infant contact can be as short as 2 years.