These analyses were undertaken to determine whether racial variation contributes to the risk of end-stage renal disease (ESRD) in close relatives of incident dialysis patients with autosomal dominant polycystic kidney disease (ADPKD)-associated ESRD. A family history of ESRD was recorded in 14,769 incident ESRD patients in Network 6 (Georgia, North Carolina, South Carolina) between September 1993 and November 1997. Two hundred thirty-seven patients with ADPKD-ESRD comprised the study population (180 white and 57 black). Differences in patient populations were analyzed using the chi-squared and Student's t-tests, and multiple regression analysis was performed. Correlation in age at ESRD onset in families was performed by linear regression analysis. A positive family history (FH) of ESRD in first- or second-degree relatives was reported by 38.6% (22 of 57) of blacks and 55% (99 of 180) of whites (P = 0.03). The 22 blacks with a positive FH had a mean of 2.0 additional ESRD relatives and 10.4 total first-degree relatives, whereas the 99 whites with a positive FH had a mean of 2.6 additional ESRD relatives and 7.0 total first-degree relatives (P = 0.14 and P < 0.001, respectively). Mean age in years at first dialysis was similar in blacks and whites, regardless of FH (black FH positive, 63.8; black FH negative, 66.3; P = 0.66; white FH positive, 60.8; white FH negative, 62.8; P = 0. 48). On average, 57.9% of the first- and second-degree relatives of white cases had ADPKD-associated ESRD, compared with 28.6% of the relatives of black cases (P < 0.001). In the multivariate analysis, white race (P = 0.004) and increasing family size (P = 0.002) were positively correlated with the number of relatives having ADPKD-associated ESRD, whereas age at ESRD onset (P = 0.50) and gender (P = 0.94) were not. Age at onset of ESRD was correlated within members of multiply affected white (P < 0.001) but not black families (P = 0.80). We conclude that blacks with ADPKD-associated ESRD are less likely than whites to have relatives with ESRD, and there is no correlation in age at onset of ADPKD-ESRD in black families.