BackgroundRacial and ethnic minority groups are less likely to have advance directives and living wills, despite the importance of advanced care planning (ACP) in end‐of‐life care. We aimed to understand the impact of an intervention to improve ACP documentation across race, ethnicity, and language on hospitalized patients at our institution.MethodsWe launched an intervention to improve the rates of ACP documentation for hospitalized patients aged >75 or with advanced illness defined by the International Classification of Diseases 10th Revision codes. We analyzed ACP completion rates, preintervention, and intervention, and used interrupted time‐series analyses to measure the differential impact of the intervention across race, ethnicity, and language.Key ResultsA total of 10,220 patients met the inclusion criteria. Overall rates of ACP documentation improved from 13.9% to 43.7% in the intervention period, with a 2.47% monthly increase in ACP documentation compared to baseline (p < .001). During the intervention period, the rate of ACP documentation increased by 2.72% per month for non‐Hispanic White patients (p < .001), by 1.84% per month for Latinx patients (p < .001), and by 1.9% per month for Black patients (p < .001). Differences in the intervention trends between non‐Hispanic White and Latinx patients (p = .04) and Black patients (p = .04) were significant.ConclusionsAn intervention designed to improve ACP documentation in hospitalized patients widened a disparity across race and ethnicity with Latinx and Black patients having lower rates of improvement. Our findings reinforce the need to measure the impact of quality improvement interventions on existing health disparities and to implement specific strategies to prevent worsening disparities.