The paper considers a process of developing evidence-based design guidelines to be used in environments where people with dementia and sight loss are living. The research involved a systematically conducted literature review and a series of consultations with people affected by dementia and/or sight loss who lived or worked in care homes or in domestic settings. Findings from the literature and the consultations were used in an iterative process to develop the guidelines. The process is outlined, providing examples from the guidelines about lighting and colour and contrast. In discussing the research findings and the development process, the authors consider implications of the work including the weakness of the evidence base, the challenges of improving this and the need for innovative approaches to understanding the complexities of design for people with dementia and sight loss. They highlight the emphasis in the literature on independence for people with sight loss and the focus on control of people with dementia, arguing that this falls short of a genuinely person-centred approach, which recognises the active participation of people with dementia and sight loss.