Key populations, including people who inject drugs, men who have sex with men, and sex workers, are disproportionately affected by HIV/AIDS and co-infections such as hepatitis C and tuberculosis. Addressing the syndemic of HIV/AIDS and co-infections requires a comprehensive, multi-sectoral approach that integrates prevention, testing, and treatment services for all relevant diseases. By adopting a syndemic approach, we can improve health outcomes, reduce transmission rates, and promote the well-being of key populations and their communities.