 This study examined the prevalence of HIV among people who have used secondary mental health services in the United Kingdom. It found that the overall point prevalence of HIV was 2.47%, which is significantly higher than the general population in the same geographic area. Additionally, the prevalence of HIV was highest among individuals with a diagnosed substance use disorder, at 3.77%. Furthermore, around two-thirds of people had their diagnosis prior to contacting mental health services, suggesting that mental health services may be a potential entry point for HIV testing and treatment. This article was authored by Robert Stewart, Amelia Jurell, Margaret Heslin, and others.