African Americans experience higher rates of chronic kidney disease (CKD) than do whites. It was hypothesized that racial differences in modifiable factors would account for much of the excess risk of CKD. A cohort study of 9082 African-American and white adults of age 30 to 74 yr, who participated in the Second National Health and Nutrition Examination Survey in 1976 to 1980 and were monitored for vital status through 1992 in the Second National Health and Nutrition Examination Survey Mortality Study, was conducted. Incident CKD was defined as treated CKD cases (ascertained by linkage to the Medicare Registry) and deaths related to kidney disease. The incidence of all-cause CKD was 2.7 times higher among African Americans, compared with whites. Adjustment for sociodemographic factors decreased the relative risk (RR) to 2.49, explaining 12% of the excess risk of CKD among African Americans. Further adjustment for lifestyle factors explained 24% of the excess risk, whereas adjustment for clinical factors alone explained 32%. Simultaneous adjustment for sociodemographic, lifestyle, and clinical factors attenuated the RR to 1.95 (95% confidence interval, 1.05 to 3.63), explaining 44% of the excess risk. Although the excess risk of CKD among African Americans was much greater among middle-age adults (30 to 59 yr of age; RR = 4.23, statistically significant) than among older adults (60 to 74 yr of age; RR = 1.27), indicating an interaction between race and age, the same patterns of explanatory factors were observed for the two age groups. Nearly one-half of the excess risk of CKD among African-American adults can be explained on the basis of potentially modifiable risk factors; however, much of the excess risk remains unexplained.