Thailand introduced universal access to Anti-retroviral treatment (ART) service in 2003. This became the main factor increasing demands for services with increasing numbers of People living with the Human Immunodeficiency Virus (HIV) and the Acquired Immune Deficiency Syndrome (AIDS), (PLHIV) and those people living longer. Since 2011, two other factors altered the ART service provision: changes in enrolment criteria to allow PLHIV with high CD4 count (a blood test that establishes the stage of immunosuppression), access to the ART service, and decentralisation changes allowing easier access to ART at peripheral levels. This study therefore examined how service providers at all levels of care deliver ART services, and developed a tool to estimate future requirements for those providers. The case study uses mixed methods including both quantitative and qualitative approaches. Two stages of data collection were conducted; fieldwork to collect data on activities and flow of ART services, and time required for each type of service provider. These become the input data for a second stage to project staffing requirements based on Markov and Monte Carlo analysis to 2025. Three models of ART services were found, across all levels of facility in the public sector operating in high HIV/AIDS prevalence settings,: community-based, doctor-led and mixed-comprehensive. All models adapted their ART services from the national guidelines by applying HR strategies: task shifting, skill mix and community-based approach, to maintain/increase accessibility and quality of care. The estimation of time required to provide ART service of providers was estimated. 60 full time equivalent (FTE) providers (doctors, nurses, pharmacists, pharmacy technicians and non-healthcare providers) in 2012, projected to almost double in 2015. This study found negligible gaps (0.02-0.05%) between needs and availability of healthcare providers to deliver ART service. The HR strategies investigated, were sufficiently widespread to be worth recommending for wide application in human resource planning. Moreover, the tool developed to estimate the requirements for healthcare providers from this study could further support forward towards planning for HIV/AIDS services in Thailand and possibly elsewhere.