The Web has attracted considerable attention as an avenue to improve healthcare delivery. This paper describes the development of a Web-based intervention support system (WISS) that helps provide tailored interventions to enhance health-related behavior change. The tailoring strategy is based on the transtheoretical model (TTM). The performance of WISS was assessed by a pilot study, a controlled randomized longitudinal experiment involving 366 multiple sclerosis (MS) patients. Results suggest that WISS can reduce MS patients' medication discontinuation rate and move more patients to a stage where dropout is least likely to occur.