Although several recent studies have documented a high incidence of end-stage renal disease (ESRD) among American Indians (AI) and Alaska Natives (AN), racial misclassification of AI/AN as members of other races on disease registries has not been accounted for. We conducted a study to link the Northwest Renal Network (NRN) ESRD database, which includes persons known to have begun dialysis in Idaho, Oregon, and Washington, and the Indian Health Service (IHS) patient registration file, which includes AI/AN enrolled for health care provided or paid for by IHS in the same states, for the period January 1, 1988 to December 31, 1990. Among the 3,356 persons included on the NRN ESRD database, 68 (2.0%) were coded as AI/AN. Of the 68 listed as AI/AN, 54 (79.4%) were identified on the IHS patient registration file. In addition to the 68 cases coded on the NRN as AI/AN, we identified 12 cases that were definitively matched to the IHS patient registration file but not coded AI/AN on the NRN. The age-adjusted annual incidence of ESRD treatment initiation among AI/AN in Idaho, Oregon, and Washington was 267.5 per million according to original racial coding on the NRN, but it increased to 311.6 per million after correction for racial misclassification. Among IHS-registered AI/AN, the annual incidence increased from 394.1 per million to 474.3 per million. Racial misclassification of AI/AN in ESRD registries may result in underestimates of AI/AN ESRD incidence for the United States.