Trends in periodontal diseases in the USA have been documented for years. However, the results have been mixed, mostly due to different periodontal assessment protocols. This study examined change in the prevalence of periodontitis between the NHANES III and the NHANES 1999–2000, and differences in the prevalence of periodontitis among racial/ethnic groups in the USA. Analysis was limited to non-Hispanic black, non-Hispanic white, and Mexican-American adults aged 18+ yrs in the NHANES III (n = 12,088) or the NHANES 1999–2000 (n = 3214). The prevalences of periodontitis for the NHANES III and the NHANES 1999–2000 were 7.3% and 4.2%, respectively. In multivariable analyses, blacks were 1.88 times (95%CI: 1.42, 2.50) more likely to have periodontitis than whites surveyed in the NHANES III. However, the odds of periodontitis for blacks and Mexican-Americans did not differ from those for whites surveyed in the NHANES 1999–2000. Our findings indicate that the prevalence of periodontitis has decreased between the NHANES III and the NHANES 1999–2000 for all racial/ethnic groups in the USA.