To describe the development, components, initial results and lessons learned from Thailand's National Access to Antiretroviral Program for People living with HIV/AIDS (NAPHA), a historical review was conducted and program monitoring was analyzed. The national antiretroviral therapy program at different levels of the public health system was implemented with all major program components; ARV protocol development, health care professional training, drug supply chain management, laboratory network formation, monitoring and evaluation, and multi-sector and PHA involvement since 2001, which was based on elements of research, pilot projects, training, national guideline development, experiences and policy making. A national monitoring system was developed to monitor the progress of the program. From February 2001 to December 2004, the monitoring reports received from implementing hospitals showed that 58,133 cases had received antiretroviral therapy (ART), and 85% (49,477) of them were continuing to take ARV drugs. In conclusion, the NAPHA was implemented nationwide with comprehensive systems. The reports indicate achievement of expansion of the ART program. Lessons learned from the program initiation and scaling up show local leadership, comprehensive training, adherence, and coordination are essential to program effectiveness and sustainability.