Registration of the ethnic origin of patients in health care is subject to political and public debate. This paper is intended to contribute to that debate. We argue that registration of the ethnic origin of all patients is a necessary condition for responsible patient care. First, similar to sex and age the ethnic origin of a patient is a relevant variable for diagnosis and treatment at the individual patient level. Second, information about the ethnic origin of patients in health care data registries is a necessary condition for good quality research on the quality of care for ethnic minority groups. This research is needed to enable adequate targeting of interventions to improve quality of care for these patients. Consequently, registration of the ethnic origin of patients is a condition for providing good care for all Dutch patients.