Objective:This is a prospective observational cohort study that aims to enroll a total of 2000 Thai MSM and TG at five health facilities in four provinces of Thailand. Each participant will be followed for 18 months. Baseline and historical rates of HIV testing/re-testing, initial CD4 counts, retention in care, and ART adherence at the study clinics, at the study clinics combined, and national data (if available) will be compared with rates after implementation of the Test and Treat strategy. Analysis will also include an assessment of HIV prevalence and incidence. This study will use similar objectives, indicators, and procedures as those used in an ongoing Test and Treat study by the Thai Red Cross AIDS Research Centre in three tertiary care hospitals, and a study to be conducted with PEPFAR Key Populations Implementation Science (KPIS) funding through United States Agency for International Development (USAID), in community-based centers, allowing comparison of uptake and follow-up of MSM and TG using the Test and Treat strategy in a variety of settings.