Objectives: There is currently little known about why people decline to participate in dyadic, psychosocial dementia research. This interview study aims to explore the reasons why people declined to participate in the Valuing Active Life in Dementia research trial. Methods: Ten family carers of people with dementia, who were part of a dyad that had declined to take part in the randomised controlled trial, participated in qualitative telephone interviews to explore their reasons for declining. Inductive thematic analysis was used to identify themes.