["Culture shapes how people understand illness and death, but few studies examine whether acculturation influences patients' end-of-life treatment preferences and medical care.", 'In this multi-site, prospective, longitudinal cohort study of terminally-ill cancer patients and their caregivers (n\u200a=\u200a171 dyads), trained interviewers administered the United States Acculturation Scale (USAS). The USAS is a 19-item scale developed to assess the degree of "Americanization" in first generation or non-US born caregivers of terminally-ill cancer patients. We evaluated the internal consistency, concurrent, criterion, and content validity of the USAS. We also examined whether caregivers\' USAS scores predicted patients\' communication, treatment preferences, and end-of-life medical care in multivariable models that corrected for significant confounding influences (e.g. education, country of origin, English proficiency). The USAS measure was internally consistent (Cronbach α\u200a=\u200a0.98); and significantly associated with US birthplace (r\u200a=\u200a0.66, P<0.0001). USAS scores were predictive of patients\' preferences for prognostic information (AOR\u200a=\u200a1.31, 95% CI:1.00-1.72), but not comfort asking physicians\' questions about care (AOR 1.23, 95% CI:0.87-1.73). They predicted patients\' preferences for feeding tubes (AOR\u200a=\u200a0.68, 95% CI:0.49-0.99) and wish to avoid dying in an intensive care unit (AOR\u200a=\u200a1.36, 95% CI:1.05-1.76). Scores indicating greater acculturation were also associated with increased odds of patient participation in clinical trials (AOR\u200a=\u200a2.20, 95% CI:1.28-3.78), compared with lower USAS scores, and greater odds of patients receiving chemotherapy (AOR\u200a=\u200a1.59, 95% CI:1.20-2.12).'] Does united state acculturation and cancer patients ' end-of-life care?