High-quality and user-friendly patient information material (PIM) is essential for understanding and accepting a new care programme. When optimising the PIM of the integrated, cross-sectoral psycho-oncological (isPO) care programme, the design of the fifth element of the patient information strategy—the patient-friendly website—was still pending. In this paper, the iterative design process of the patient-friendly isPO website is described. We applied the participatory health research (PHR) approach to enable high levels of participation of its respective end-users (e.g., cancer survivors), service providers, and experts. The design included six steps: (1) initiation, (2) planning, (3) initial idea exploration, (4) creation of a first working version, (5) three optimisation loops, and (6) dissemination. An exploratory mixed-methods design has been used. Qualitative data collection included document analysis, interviews, and participatory action research (PAR) loops with focus groups. Finally, the quality of the newly designed website was quantitatively assessed with the UPIM-Check, a user-friendly instrument for assessing and optimising PIM. The PHR approach was indispensable for the design of our needs-oriented, patient-friendly website. Participants’ high levels of participation strongly contributed to the products’ quality. The final descriptive statistical evaluation shows that the final website was rated very good on average by its end-users.