AimsWe aimed to ascertain the content validity of an instrument to assess health and social care professionals' knowledge and attitudes towards later‐life intimacy and sexuality (HSCP‐KALLIS).BackgroundFor older adults, intimacy and sexuality are important in maintaining their quality of life and well‐being. However, addressing these needs remains challenging for health and social care professionals, particularly for nursing staff providing 24‐h direct care to older people with dementia or those identified as lesbian, gay, bisexual, transgender, intersex or queer/questioning individuals. Existing instruments assessing knowledge and attitudes towards later‐life intimacy and sexuality are dated and fail to adequately address dementia and sexual diversity.DesignA two‐round modified Delphi study was conducted.MethodsInitially, 79 knowledge and attitude items were generated through an integrative review. Panellists rated each item's clarity and importance using online questionnaires. The content validity index for the individual and overall items was calculated. The panellists' written feedback—along with their knowledge level of later‐life intimacy and sexuality—was obtained.ResultsPanellists included health and social care professionals (n = 9); healthcare‐related educators (n = 2); researchers specialising in later‐life intimacy, sexuality, dementia care and sexual diversity support (n = 7); and family carers of older people with dementia (n = 2). The instrument was revised based on the feedback received. The components of dementia, LGBTIQ+ and the provision of sex worker services in healthcare settings were highlighted by the panellists. Notably, 46 knowledge and 40 attitude items fulfilled the consensus criteria for clarity and importance.ConclusionsAcceptable content validity was established for the knowledge and attitude items. Further research is required to establish the psychometric properties of the HSCP‐KALLIS. This instrument has implications for clinical practice—specifically, in nursing care—by addressing issues to improve awareness regarding later‐life intimacy and sexuality in healthcare settings.Implications for PracticeThe HSCP‐KALLIS has the potential to inform the educational needs regarding knowledge and attitudes towards later‐life intimacy and sexuality for health and social care professionals, specifically nursing staff. The findings of the HSCP‐KALLIS can be used for the development of competencies for later‐life intimacy and sexuality, establishing policies and guidelines to support older adults’ intimacy and sexuality needs in health care settings.