The racial disparity in the incidence of ESRD exemplified by the three- to four-fold excess risk among black compared with white individuals in the United States is not reflected in the prevalence of less severe degrees of impaired kidney function among black compared with white individuals. The four-variable Modification of Diet in Renal Disease study equation was used to evaluate the black-to-white prevalence of impaired kidney function with increasing severity of impairment among participants in the Reasons for Geographic and Racial Differences in Stroke (REGARDS) study, a nationally representative, population-based cohort of individuals who are 45 yr and older. An estimated GFR (eGFR) <60 ml/min per 1.73 m2 was present in 43.3% of the 20,667 REGARDS participants and was slightly less prevalent among black than white patients (33.7 versus 49.9%; prevalence odds ratio 0.51; 95% confidence interval [CI] 0.48 to 0.54). The lower prevalence among black patients was not uniform as eGFR declined. After controlling for other patient characteristics, the black-to-white odds ratio was 0.42 (95% CI 0.40 to 0.46) at an eGFR of 50 to 59 ml/min per 1.73 m2 and increased to 1.73 (95% CI 1.02 to 2.94) at an eGFR of 10 to 19 ml/min per 1.73 m2. The disparity in prevalence of impaired kidney function among white compared with black patients reversed as the severity of impaired kidney function increased. Factors that are responsible for the increasing prevalence of severely impaired kidney function among black patients remain to be determined. Copyright © 2006 by the American Society of Nephrology.