BACKGROUNDHealth care disparities have been identified in the treatment of older and racial/ethnic minority breast carcinoma patients. The purpose of the current study was to examine racial/ethnic group differences in the treatment decision‐making process of older breast carcinoma patients and the differential impact on treatment received.METHODSA cross‐sectional survey was conducted of a population‐based, consecutive sample identified by the Los Angeles Cancer Surveillance Program comprised of Latina (n = 99), African‐American (n = 66), and white (n = 92) women age ≥ 55 years (total n = 257) and who were between 3–9 months after their primary breast carcinoma diagnosis.RESULTSApproximately 49% of less acculturated Latinas and 18% of more acculturated Latinas indicated that their family members determined the final treatment decision, compared with less than 4% of African‐Americans and whites (P < 0.001). This disparity remained in multiple logistic regression analysis, controlling for potential confounders, including sociodemographic, physician–patient communication, social support, and health variables. Compared with African‐American and white women, Latina women were more likely to identify a family member as the final treatment decision‐maker (adjusted odds ratio [AOR] of 7.97; 95% confidence interval [95% CI], 2.43–26.20, for less acculturated Latinas; and AOR of 4.48; 95% CI, 1.09–18.45, for more acculturated Latinas). A multiple logistic regression model, controlling for sociodemographic and health characteristics, indicated that patients were less likely to receive breast‐conserving surgery (BCS) when the family made the final treatment decision (AOR of 0.39; 95% CI, 0.18–0.85).CONCLUSIONSFamily appears to play a powerful role in treatment decision‐making among older Latina breast carcinoma patients, regardless of the level of acculturation. This family influence appears to contribute to racial/ethnic group differences in treatment received. Physicians should acknowledge and educate patients' family members as potential key participants in medical decision‐making, rather than merely as translators and providers of social support. Cancer 2006. © 2006 American Cancer Society.