ABSTRACT Improved screening for sexually transmitted infections (STI) is essential to reversing the STI epidemic in the United States (US). Nearly half of STIs in the US occur in adolescent and young adults (AYA) aged 15-24, and failure to perform genitourinary and extra-genital (anorectal and oropharyngeal) STI testing contributes to the propagation of disease. Emergency Departments (ED) care for over 17 million AYA each year, the majority being poor and minority. Our prior work demonstrated the inconsistent use of contraceptives among this population, and how, although ED providers are receptive to ED-based sexual health interventions, implementation barriers persist, such as limited time and resources. Innovative interventions are needed that fit efficiently within the ED workflow and maximize appropriate STI testing. One such intervention would be a patient decision aid that informs and empowers AYA patients who may benefit from STI testing. Patient decision aids have been used to successfully facilitate shared decision-making in the ED for various clinical scenarios. We have gathered a multi- disciplinary team of experts in pediatric, adult, and emergency medicine, ED-based clinical trials, digital health, implementation science, biostatistics, and shared decision-making to develop STIckER (STI ChecK in the ER), an evidence-based, digital patient decision aid to facilitate STI testing in the ED using a shared decision-making approach. STIckER consists of three steps: (1) the patient “scanning the sticker” via a QR code leading to a non- judgmental sexual health screening assessment; (2) shared decision-making educational modules connecting personalized STI risk to evidence-based testing recommendations; and (3) facilitation of a patient-provider STI testing conversation using a confidential, color-coded digital infographic. The specific aims of this proposal are (1) To refine “STIckER,” our STI testing patient decision aid through an iterative development approach based on stakeholder feedback; (2) To conduct usability testing and finalize development of STIckER; and (3) To conduct a pilot randomized trial to examine the preliminary efficacy and implementation of STIckER in the ED. We hypothesize that sexually active AYA who interact with STIckER will more often undergo any STI testing compared with sexually active AYA who do not interact with STIckER. SIGINIFICANCE: An effective, automated digital intervention increasing STI testing can be utilized in other EDs as a reproducible means to promote the provision of evidence-based sexual health education, decrease STI rates, and improve AYA health outcomes throughout the US.