ABSTRACT: Importance:Advance care planning improves the receipt of medical care aligned with patients' values; however, it remains suboptimal among diverse patient populations. To mitigate literacy, cultural, and language barriers to advance care planning, easy-to-read advance directives and a patient-directed, online advance care planning program called PREPARE For Your Care (PREPARE) were created in English and Spanish. Objective:To compare the efficacy of PREPARE plus an easy-to-read advance directive with an advance directive alone to increase advance care planning documentation and patient-reported engagement. Design, Setting, and Participants:A comparative efficacy randomized clinical trial was conducted from February 1, 2014, to November 30, 2017, at 4 safety-net, primary-care clinics in San Francisco among 986 English-speaking or Spanish-speaking primary care patients 55 years or older with 2 or more chronic or serious illnesses. Interventions:Participants were randomized to PREPARE plus an easy-to-read advance directive (PREPARE arm) or the advance directive alone. There were no clinician-level or system-level interventions. Staff were blinded for all follow-up measurements. Main Outcomes and Measures:The primary outcome was documentation of new advance care planning (ie, legal forms and/or documented discussions) at 15 months. Patient-reported outcomes included advance care planning engagement at baseline, 1 week, 3 months, 6 months, and 12 months using validated surveys. Intention-to-treat analyses were performed using mixed-effects logistic and linear regression, controlling for time, health literacy, and baseline advance care planning, clustering by physician, and stratifying by language. Results:Among the 986 participants (603 women and 383 men), the mean (SD) age was 63.3 (6.4) years, 387 of 975 (39.7%) had limited health literacy, and 445 (45.1%) were Spanish speaking. No participant characteristic differed between the 2 groups, and retention was 85.9% (832 of 969) among survivors. Compared with the advance directive alone, PREPARE resulted in a higher rate of advance care planning documentation (unadjusted, 43.0% [207 of 481] vs 33.1% [167 of 505]; P?