The HIV/AIDS epidemic which broke out in Thailand 1988 was mainly caused by the widespread patronage of prostitutes. The Thai authorities responded with programmes which encouraged the use of condoms in commercial sex. These programmes were highly successful. However, prostitution has changed since the beginning of the epidemic, partly for economic and demographic reasons, but mainly because of the fear of AIDS. Fewer women practise prostitution, men patronize it less, and the price of commercial sex has risen. Prostitution is less likely to be practised in brothels and more likely to be practised in establishments like restaurants and bars. Moreover, as fewer native Thai women are willing to practise prostitution, foreign women are taking their place. In order to continue to control the epidemic, the authorities will have to adapt their programmes to the changing structure of commercial sex.