This case study discusses the design, development, and formative evaluation of Epilepsy Journey, an individually tailored, web-based intervention designed to address the unique executive functioning (EF) needs of adolescents with epilepsy. This intervention was designed through a three-phase iterative, patient-centered participatory action research process. First, a front-end analysis was completed to identify the unique needs of adolescents with epilepsy and initial design ideas via focus groups. Second, a preliminary design of the intervention was developed from focus group results. Finally, we iteratively incorporated revisions and refinements based on patient-centered feedback collected during usability sessions. Findings based on usage analytics, user reports, and coded qualitative themes from usability sessions suggest that our iterative, patient-centered approach to design, development, and evaluation resulted in a visually appealing interactive and brief intervention that is both engaging and individually tailored to the needs of adolescents with epilepsy.