BackgroundThe Internet should be suitable for delivery of interventions targeting young cancer patients. Young people are familiar with the technologies, and this patient group is small and geographically dispersed. Still, only few psycho-educational Web-based interventions are designed for this group. Young cancer patients consider reproductive health, including sexuality, an area of great importance and approximately 50% report sexual problems and fertility-related concerns following cancer treatment. Therefore, we set out to develop a self-help Web-based intervention, Fex-Can, to alleviate such problems. To improve its quality, we decided to involve patients and significant others as research partners. The first 18 months of our collaboration are described in this paper. The intervention will subsequently be tested in a feasibility study followed by a randomized controlled trial.ObjectiveThe study aims to describe the development of a Web-based intervention in long-term collaboration with patient research partners (PRPs).MethodsTen former cancer patients and two significant others participated in building the Web-based intervention, using a participatory design. The development process is described according to the design step in the holistic framework presented by van Gemert-Pijnen et al and evaluates the PRPs’ impact on the content, system, and service quality of the planned intervention.ResultsThe collaboration between the research group and the PRPs mainly took place in the form of 1-day meetings to develop the key components of the intervention: educational and behavior change content, multimedia (pictures, video vignettes, and audios), interactive online activities (eg, self-monitoring), and partial feedback support (discussion forum, tailored feedback from experts). The PRPs influenced the intervention’s content quality in several ways. By repeated feedback on prototypes, the information became more comprehensive, relevant, and understandable. The PRPs gave suggestions concerning the number of exercises and pointed out texts and pictures needing revision (eg, experienced as normative or stereotypical) to increase the persuasiveness of the program. The system quality was improved by PRPs’ feedback on design, technical malfunctions, and navigation on the website. Based on feedback about availability of professional support (technical problems and program content), the organization for support was clarified, which increased service quality. The PRPs also influenced the research project on an overall level by suggesting modifications of inclusion criteria for the RCT and by questioning the implementation plan.ConclusionsWith suggestions and continuous feedback from PRPs, it was possible to develop a Web-based intervention with persuasive design, believed to be relevant and attractive for young persons with cancer who have sexual problems or fertility distress. In the next step, the intervention will be tested in a feasibility study, followed by an RCT to test the intervention’s effectiveness in reducing sex...