Background The carer‐delivered individual cognitive stimulation therapy (iCST) was developed to improve cognition and quality of life of people with dementia. This study aims to explore people with dementia and family carers' concepts of mental stimulation and experiences of participating in the iCST intervention. Methods A sub‐sample of 23 dyads of people with dementia and their family carers who completed the iCST intervention took part in semi‐structured in‐depth interviews. Data were analysed using framework analysis. Results Three main themes emerged, ‘Concepts of mental stimulation’, ‘Experiencing changes in everyday life as a result of participating in iCST’ and ‘Carer adherence to the intervention’ along with 10 sub‐themes. The overall experience of participating in iCST was described as having opportunities to engage in enjoyable mentally stimulating activities, motivation to stay active and bringing people with dementia and their carers ‘together’. Family carers mentioned that finding time to do the sessions and their relatives being reluctant to engage in the activities could hinder their participation in the intervention. Conclusions People with dementia and their family carers found iCST stimulating and enjoyable, but many had difficulty delivering all the sessions as planned. Family carers suggested that providing extra support by involving other people in delivering the intervention may help to improve adherence to the intervention. iCST may be a useful tool to encourage people with dementia and their carers to communicate. © 2017 The Authors. International Journal of Geriatric Psychiatry Published by John Wiley & Sons Ltd.