This is a cross-sectional quantitative study carried out with 241 elderly diagnosed with HIV, assisted in the services of reference of Recife, Pernambuco State, Brazil. Knowledge and attitudes were evaluated through the Aging Sexual Knowledge and Attitudes Scale (ASKAS). Senior men, participants with higher educational level, those without depressive symptoms and individuals diagnosed with HIV for more than 12 years have a higher level of knowledge about sexuality in old age. Conservative attitudes toward sexuality in aging have been strongly associated with women, illiterate participants, practicing evangelical and Catholic religions, and elderly diagnosed with HIV with less than 12 years. Elderly with less knowledge had more conservative attitudes regarding sexuality in aging (r = 0.42; p < 0.0001). Thus, it is essential to carry out health actions with the aim of improving knowledge and attitudes regarding sexuality in the elderly, paying particular attention to those who are most vulnerable to HIV infection.