Globally, the elderly population is aging and changing in composition with the over 50 years of age constitutes the fastest-growing segment of the aged population. There has been scanty evidence indicating that sexual risk-taking behavior is no longer confined to young population ages (15-49) years but among vulnerable older people as well. The study aims to investigate on Knowledge, Attitudes and Practices on HIV/AIDS and other selected STIs among persons aged 50 years and over. This is a cross-sectional facility-based study with qualitative analysis on responses obtained from 356 randomly selected patient participants 50 years and over visiting selected health facilities in Nairobi County in Kenya. Overall assessment of the knowledge on symptoms of STI score revealed that 12.1% of the participants scored ‘good’ on knowledge of symptoms of STI, 89.0% scoring (Good) in attitude on prevention against contracting HIV and 40.5% scored high on the risky sexual practices of contracting HIV. Little knowledge is more likely to render participants unprotected due to potential risks to condom use - difficulties in communication between partners, concern for lack of trust, and feelings that the male partner controls condom use.