ABSTRACT Pediatric clinical trials are important for discovering effective medicines, treatments, devices, and interventions designed for children and adolescents. However, recruitment and retention in pediatric clinical trials remains a challenge. Enrollment in clinical trials requires both consent of the parent and assent of the youth and the roles that each takes and the contributions that each makes in the decision-making process can vary, especially across development. When children are younger, parents are more likely to decide whether or not their child will participate in a clinical trial. As children mature, the decision-making process typically shifts to become more collaborative between parents and adolescents. There is evidence that both parents and adolescents prefer a shared decision-making (SDM) approach to clinical trial participation; however, there are few studies that directly examine the parent-child communication behaviors that are a part of the decision- making process. The proposed project will address this gap through the use of videotaped observations, questionnaires, and semi-structured interviews. A diverse sample of parent-adolescent pairs (N=80) will be observed making the decision whether to participate in two different types of hypothetical pediatric clinical trials (i.e., high-risk; low-risk). Following each discussion, pairs will complete self-report questionnaires about the experience. Positive (e.g., complimenting) and negative communication (e.g., sarcasm) behaviors will be coded. Aim 1 will examine how positive and negative communication behaviors relate to parent and adolescent decision-making involvement, communication satisfaction, and likelihood to participate in the trials. Given the dyadic nature of the decision-making process, an Actor-Partner-Interdependence Model framework will be applied to explore the unique and dyadic effects of parent-child communication on pediatric clinical trial decision-making. In addition, a subgroup (N=20) of parent-teen pairs from the observational study will be purposively sampled to participate in follow-up interviews. Adolescents’ report of communication satisfaction will be used to identify pairs that experienced the most positive and negative decision-making experiences. This approach will allow us to gather the most information-rich data from experiences on both sides of spectrum. The proposed project will provide novel information about the specific communication behaviors that parents and adolescents engage in as part of the decision-making process and how these behaviors impact their final decisions and satisfaction with the process. The findings from this project have the potential to inform the development of education resources or decision aids that can support families in engaging in more effective shared decision-making practices with their developing adolescent when provided with the opportunity to participate in a pediatric clinical trial.