HIV Epidemic Among Men Who Have Sex with Men (MSM) and Transgender Women (TGW) in Sarawak, Malaysia: An analysis from the Integrated Biological and Behavioural Surveillance (IBBS) Lite 2024 Introduction Men who have sex with men (MSM) and transgender women (TGW) are among the key populations affected by the HIV epidemic in Sarawak, Malaysia. The objective of this study was to determine HIV prevalence and associated behaviour among MSM and TGW in Sarawak. Methods Respondent-driven sampling (RDS) was used to recruit MSM and TGW between June and August 2024. The study consisted of two components. The first component was a behavioural survey, conducted through a selfadministered online questionnaire via a web-based platform. The second component involved biological testing, where respondents were instructed to visit a community-based testing site of their choice for blood testing after completing the online survey. Statistical analysis was performed in RStudio using the Gile's Successive Sampling Estimator. Results This study recruited 217 MSM and 151 TGW. Consistent condom use among both groups remains low. While most MSM and TGW reported recent HIV testing, Hepatitis C testing and treatment rates are still low. HIV prevalence in Sarawak was 9.5% (95% CI: 2.9, 16.0) among MSM and 10.1% (95% CI: 1.8, 18.5) among TGW, with syphilis prevalence among MSM reaching a concerning 12% (95% CI: 1.8, 22.3). Conclusions In conclusion, improving HIV prevention and care for MSM and TGW in Sarawak requires promoting condom use, increasing awareness of Hepatitis C, and including substance use interventions in HIV programs. Community outreach using culturally sensitive approaches is crucial to improving access to services and building trust. Furthermore, integrating syphilis management into HIV prevention efforts is critical, given its strong association with increased HIV risk. Findings highlight the need for targeted interventions and continued surveillance among key populations in Sarawak to ensure a sustained and effective public health response.