In Thailand, a national program to prevention mother-to-child HIV transmission began in 2000. Elements of the program included voluntary counseling and HIV testing of pregnant women, a short course of zidovudine for HIV-infected women and their infants, and formula feeding for infants. Research, monitoring and evaluation of pilot projects, training and policy-making provided an essential foundation for the program. The authors estimate that further implementation of the program could reduce the risk of mother-to-child HIV transmission from 30 percent to less than 10 percent.