Understanding and eliminating health disparities requires accurate data on race/ethnicity. To assess the quality of race/ethnicity data, we compared medical record classifications to self-report of a study of prophylactic mastectomy. A total of 788 women had race/ethnicity from both sources; 69.9% were 55 years of age or older, 38.3% were at least college graduates, and 67.8% were married or living with someone. There were 817 race/thnicity classifications for the 788 women, of which 758 (92.3%) were identical in the medical record and self-report. Sensitivity and positive predictive value were high (86.7%-97.2%) for whites, Asians, and blacks and moderate (64.0% and 68.1%) for Latinas. However, only one of 18 Native Americans was correctly identified in her medical record. Our results indicate that even if the overall accuracy of medical record classifications for race/ethnicity is high, such a finding may obscure substantial inaccuracies in the recording for racial/ethnic minorities, especially Latinas and Native Americans.