Improving cognition is service users' top research priority for life after stroke, and future research should include outcomes that they deem important. Patient perspectives on outcomes are collected using patient-reported outcome measures (PROMs). There is currently no patient-centred PROM specific for cognitive rehabilitation trials. Inform PROM development by exploring stroke survivor perspectives on the important, measurable impacts of persisting post-stroke cognitive problems. Qualitative semi-structured interviews in participants' homes. Purposive sample of 16 cognitively impaired stroke survivors at least six months post-stroke. Interviews used a schedule and communication aids developed through patient consultation. Interviews were transcribed verbatim with non-verbal communication recorded using field notes. Data were analysed using a framework approach to find commonalities to shape the focus and content of an outcome measure. Participants identified important impacts of their 'invisible' cognitive problems, outside of other stroke-related impairments. Cognitive problems exacerbated emotional issues and vice versa. Changes in self-identity and social participation were prominent. Impact was not spoken about in terms of frequency but rather in terms of the negative affect associated with problems; terms like 'bothered' and 'frustration' were often used. The results support the development of a PROM specifically designed to address the impact of cognitive problems. It should: include items addressing a comprehensive range of cognitive skills; ask questions about mood, self-identity and social participation; use accessible wording that respondents understand and endorse; measure impact rather than frequency; and explore perceived impact on carers.