||Every year, over two million people are diagnosed with skin cancer. The primary method recommended for skin cancer prevention is reducing ultraviolet radiation (UVR) exposure. However, consistent daily sun protection is often inadequate, even among higher risk patients. This study tested both 1) the effectiveness of a daily, online intervention that provided color-coded feedback illustrating duration of UVR exposure on specific body sites, and 2) theoretically derived predictions regarding the process of reducing UVR exposure in response to feedback. Participants (n=47; 53.3% women, mean age=49.87) were recruited from dermatology clinics and had an elevated risk of skin cancer. The majority (63.8%) had a history of skin cancer, including 44.7% with melanoma. At baseline, then 1 and 2 months later, sun exposure was assessed by reflectance spectroscopy, an objective measure of skin color, and by the self-report Minutes of Unprotected Sun Exposure (MUSE) Inventory. Participants were randomly assigned to either a feedback, self-monitoring, or control condition. For feedback participants, the 14-day intervention included daily sun-protection reminders, the MUSE Inventory, color-coded feedback diagrams, and survey items on health-relevant cognitions and emotions. To control for the potential benefit of reporting one's behavior, self-monitoring participants completed these assessments but did not receive feedback. Control participants only received daily reminders. On the MUSE Inventory, feedback participants reported less sun exposure than self-monitoring participants during the intervention. In these conditions, higher perceptions of goal fulfillment for sun exposure occurred when reported sun exposure was lower and these perceptions predicted higher self-efficacy for sun protection. Only feedback participants reported decreased sun exposure at the 2-month follow-up; significant decreases in sun exposure were reported in the lower face, arms, and lower legs, which are common sites for melanoma. Reflectance spectroscopy measurements did not change over time or by condition, potentially because they were taken on a limited number of body sites (wrist, upper face) for which exposure did not decrease substantially. This study supports the feasibility and effectiveness of an online, daily feedback intervention for sun exposure among higher risk patients. Future directions include testing it among less compliant populations and investigating additional mechanisms (e.g., changes in goals) through which feedback operates.