Background/Aims: Behavioral nudges in the food environment increase healthy choices, but it is unknown if they improve diet and health. The ChooseWell 365 study will determine if an automated, personalized worksite intervention to nudge healthier choices improves overall diet and cardiometabolic health. Design: Randomized controlled trial of 602 hospital employees who regularly use on-site cafeterias and pay with an employee ID. Intervention: The intervention combines an environmental strategy (traffic-light labeling) with objective feed- back and personalized nudges (health/lifestyle tips, social norms, incentives) to promote healthy food choices. The ChooseWell 365 software platform automatically generates personalized emails and letters that integrate employees' weight goals with health, lifestyle, and cafeteria purchasing data. Over one year, the intervention group receives two weekly emails. One provides a log of daily purchases; the second provides personalized health/lifestyle tips. The intervention group receives monthly mailed letters with social norm comparisons and financial incentives for healthier purchases. The one-year intervention will be completed in February 2019; all follow-up will be completed March 2020. Outcomes: Weight, cardiometabolic risk factors, and dietary intake at one and two-year follow-up. Other out- comes include worksite food purchases by study participants and other non-participant employees who are socially connected (inferred from purchasing data) to participants.Conclusions: ChooseWell 365 tests a novel strategy to deliver a scalable worksite prevention program that is integrated into the workday. The intervention is personalized but automated and therefore does not require costlier individual counseling. In the future, this program could be applied broadly in other worksite settings.