Computer-assisted interventions represent an innovative approach to adolescent smoking cessation that may offer advantages over traditional smoking interventions in their potential to provide adolescents with a variety of appropriate cessation-related activities, as well as interactive feedback tailored to their developmental, psychosocial, behavioral, and biological needs. As part of a larger project to evaluate the effectiveness of an Internet-based approach to smoking cessation among adolescents, this paper will describe the intervention development process. Stomp Out Smokes (S.O.S.), an Internet-based information and support system, was created to address the specific needs and experiences of adolescents who want to quit smoking. The development of S.O.S. involved an iterative process with five distinct yet often overlapping phases: Phase 1: review of the adolescent development, smoking cessation, and health literature; Phase 2: development and implementation of a needs assessment; Phase 3: construction of a site development strategy; Phase 4: development, review, and revision of content; and Phase 5: development of the website architecture and graphic design.