OBJECTIVES: While trends in tooth loss among older adults have been well documented and show a decline over the last few decades, little is known about trends in tooth decay which may lead to tooth loss. The study aim was to examine trends in tooth decay among adults ages 50 years and older in the United States and determine whether these trends were consistent across demographic and socioeconomic subgroups of middle-aged and older adults. METHODS: Secondary analysis of data collected through detailed oral health examinations in the National Health and Nutrition Examination (NHANES) surveys 1988-1994 and 1999-2004. Tooth decay was measured as active caries. Multivariable associations were estimated using negative binomial regression models. RESULTS: Averaged over time, the mean number of decayed teeth was 0.54. Rates of decay remained stable over time. Males, non-Hispanic Blacks, Mexican-Americans, and those of other race/ethnicity as well as those with fewer years of education and lower levels of income had more decayed teeth. The increased number of decayed teeth for Mexican-Americans and those of other race/ethnicity was due in part to differing levels of education and income. Trends over time did not vary by any of these demographic and socioeconomic characteristics. Trends in the number of decayed teeth did not meaningfully change when the numbers of missing and filled teeth were controlled. CONCLUSIONS: Although studies have shown the number of middle-aged and older Americans experiencing tooth loss has decreased over time, trends in tooth decay have remained relatively stable, with socioeconomic disparities persisting over time.