Background: Sleep disorders, including insomnia, are widespread problems, which have increased during the COVID-19 pandemic. Guidelines for the treatment of insomnia prioritize non-pharmacological interventions. Nevertheless, primary care professionals lack well-developed material for patient education, that could help implement the treatment guidelines in Flanders, Belgium.Objective: This project's purpose is to develop complementary, written educational material, grounded in the principles of evidence-based practice, for primary care.Patient Involvement: This co-design project involved patients and health professionals. Special attention was given to including patients with low health literacy, and empowering patients when designing in mixed groups.Methods: Based on the framework of Sanders and Stappers (2014), data were collected and analyzed in four phases. Pre-design, needs were explored using think-aloud studies and focus groups. Next, for generative pur-poses, the design studio method was used. Then, evaluation of the prototype happened with another series of think-aloud studies. Finally, post-design, implementation of the product was evaluated with a short survey. Results: Twenty-five participants (10 patients and 15 healthcare professionals) contributed to the development of an educational patient leaflet called Sssssst. How do you sleep (at night)? Out of 30 professionals who received the printed leaflet for use in practice, 17 provided feedback after six months. Generally, the leaflet was well received. Visual design aspects stimulated use in practice.Discussion: Written and visual materials aid primary care professionals to educate patients on sleep and insomnia. This supporting tool also stimulates self-management in patients. Although inspiring and educational for all stakeholders, a co-design approach is no guarantee for the product to fit all.