For health care planning and policy, it is important to determine whether socio-economic disparities in edentulism, an ultimate marker of oral health, have improved over time. The aim of this study was to investigate the socio-economic disparities in edentulism between 1972 and 2001. Representative samples of the United States population, 25-74 years old, were obtained from NHANES I (1972), III (1991), and 1999-2002. Differences in the edentulism prevalence between high and low socio-economic positions (SEP) were compared. Differences in edentulism prevalence remained stable over approximately three decades (p = 0.480), being 10.6 percentage points in 1972, 12.1 percentage points in 1991, and 11.3 percentage points in 2001. Exploratory subgroup analyses suggested that disparities decreased for those individuals reporting a dental visit in the prior year and those reporting never having smoked. In conclusion, the absolute prevalence difference in edentulism between low and high socio-economic positions has remained unchanged over the last three decades.