This study aims to establish an understanding of (a) health-care professionals’ knowledge and attitudes; and (b) tools used to assess sexuality in older people living with/(out) dementia and those identified as lesbian, gay, bisexual, trans, or intersex (LGBTI) individuals. An integrative review of the literature, as registered on the PROSPERO international Prospective Register of Systematic Reviews (CRD42019129589), was conducted. A comprehensive and systematic literature search was performed for the period between 2009 to 2019 across eight electronic databases: CINAHL, PubMed, MEDLINE, Web of Science, Cochrane library, Embase, PsycINFO, and Scopus, together with a manual search of reference lists. Screening of titles, abstracts, and full texts of eligible studies plus quality appraisal (using the Mixed Methods Appraisal Tool) were independently conducted by two reviewers with disagreements resolved via discussion with a third reviewer. Nineteen articles were reviewed with three themes identified from the synthesis: 1) varying knowledge and attitudes amongst health-care professionals; 2) needs for professional development opportunities and support from workplace and 3) lack of recent validated tools to assess knowledge and attitudes. Health-care professionals’ knowledge and attitudes toward sexuality in older people living with/(out) dementia and those identified as LGBTI individuals are varying. Sexuality education and professional development training are needed to enhance their knowledge and attitudes and build skills in order to manage sexuality concerns. Current assessment tools are inadequate, highlighting the need for an appropriate assessment tool to be developed.