People are living longer and are affected by challenging chronic, lifestyle- and age-related conditions such as dementia and stroke. The increasing number of people living with challenging health conditions highlights so-cial concerns and their implications for the successful delivery of healthcare services. Research on improving dementia care [1] shows a need to involve people living with dementia, their families, and health and social care professionals when designing improvements to their healthcare ser-vices. In addition, involving patients recovering from stroke in discussions about rehabilitation services has been considered important to enable mak-ing decisions that better address their health care needs [2]. This paper pre-sents two case studies of a participatory co-design approach used to engage people; a) living with dementia, and b) recovering from stroke in design re-search, where co-design-led methods were used to enable participation. The paper describes the importance of each of the roles of – and relationships between – individuals involved in the participatory co-design research pro-cess and how people living with challenging health conditions are enabled to participate in a form of three-way relationship. It discusses lessons learned, reflections and recommendations for a new collaborative model for people living with challenging health conditions engagement to enable a more equal and reciprocal partnership for participation in design research into healthcare improvements.