Background: Racial/ethnic minorities are more likely to report receipt of lower quality of health care; however, the mediators of such patient reports are not known. Objectives: To determine (1) whether racial disparities in perceptions of quality of health care are mediated by perceptions of being discriminated against while receiving medical care and (2) whether this association is further mediated by patient sociodemographic characteristics, access to care, and patient satisfaction across racial/ethnic groups. Research Design: A cross-sectional analysis of a population-based sample of California adults responding to the 2003 California Health Interview Survey. Multivariable logistic regression was used to examine the relationship between perceived discrimination and perceived quality of health care after adjusting for patient characteristics and reports of access to care. Main Results: A total of 36,831 respondents were included. African Americans (68.7%) and Asian/Pacific Islanders (64.5%) were less likely than non-Hispanic whites (72.8%) and Hispanics (74.9%) to rate their health care quality highly. African Americans (13.1%) and Hispanics (13.4%) were the most likely to report discrimination, followed by Asian/Pacific Islanders (7.3%) and non-Hispanic whites (2.6%). Racial/ethnic discrimination in health care was negatively associated with ratings of health care quality within each racial/ethnic group, even after adjusting for sociodemographic variables and other indicators of access and satisfaction. Feeling discriminated against fully accounted for the difference in low ratings of quality care between African Americans and whites, but not for other racial/ethnic minorities. Conclusions: Patient perceptions of discrimination may play an important, yet variable role in ratings of health care quality across racial/ethnic minority groups. Health care institutions should consider how to address this patient concern as a part of routine quality improvement. © 2010 Society of General Internal Medicine.