Background <p>The Experimental EQ Health and Wellbeing 9 (EQ-HWB-9) is a generic measure developed to assess the impact of health, social care and informal caregiving on quality of life. Several modifications have been proposed based on emerging evidence. This study aimed to assess the content validity of these modifications and user preferences.</p> Method <p>Individuals with a long-standing physical or mental health condition or disability were invited from an online panel ensuring gender balance and age coverage. Two interviewers conducted semi-structured cognitive interviews to assess comprehensibility, relevance, and comprehensiveness of the modified experimental EQ-HWB-9 v1.2. Participants’ views on differences between the modified and original experimental versions, as well as their preferences, were explored. Interviews were conducted via videoconferencing, recorded and transcribed verbatim. Framework analysis was used to code interviews, with themes drawn from the literature and data.</p> Results <p>Twenty-six interviews were completed. Half the participants were female; participant age ranged from 24 to 68 years. Six of the nine items (‘activities’, ‘exhausted’, ‘lonely’, ‘difficulty concentrating/thinking clearly’, ‘anxious’, ‘sad/depressed’) were understood as intended by all participants. Some comprehension issues arose with the ‘mobility’ and ‘pain_severity’ items. Participants generally preferred the modified version, though a clear majority was not always observed. Justifications focused on item appropriateness, readability and distress.</p> Discussion and conclusion <p>As a generic measure, EQ-HWB-9 v1.2 performed well for comprehension, relevance and comprehensiveness. Modifications were well accepted and, except for the use of item stem, preferred over the original version. These findings will be combined with other international evidence to support finalising the instrument.</p>