Objective. - To determine reasons for the 4-fold higher incidence of treated end-stage renal disease (ESRD) in African-American men compared with white men. Design. - Prospective study. Setting. - Men screened in 1973 through 1975 for entry into the Multiple Risk Factor Intervention Trial (MRFIT). Participants. - A total of 332 544 men (300 645 white, 20 222 African American, and 11 677 other ethnic groups) aged 35 to 57 years. Main Outcome Measures. - Incidence of ESRD assessed through 1990 using the Health Care Financing Administration national ESRD treatment registry and by surveillance for death from renal disease from data of the National Death Index and the Social Security Administration. Results. - Over a mean follow- up of 16 years, age-adjusted ESRD incidence was 13.90 per 100 000 person- years in white men and 44.22 per 100 000 person-years in African-American men. Higher blood pressure and lower socioeconomic status were associated with higher incidence of ESRD in both ethnic groups. With adjustment for baseline age, systolic blood pressure, number of cigarettes smoked, previous myocardial infarction, diabetes, income, and serum cholesterol level, relative risk of ESRD in African-American men compared with white men was reduced from 3.20 to 1.87 (95% confidence interval, 1.47-2.39). Both higher systolic blood pressure and lower income in African-American men as compared with white men were particularly related to this reduced relative risk. Results were similar when hypertensive ESRD was used as the outcome. Conclusion. - Both higher blood pressure and lower income are associated with a higher incidence of ESRD in both white and African-American men. Disparities in blood pressure and socioeconomic status relate importantly to the excess risk of ESRD in African-American men compared with white men.