Several sexually transmitted diseases are endemic in the tropics. The morbidity and mortality from the human immunodeficiency viruses (HIV-1 and HIV-2) alone now rival that caused by Plasmodium falciparum malaria in several African and Asian nations. The genital ulcers of chancroid and syphilis facilitate the sexual transmission of HIV. Within the last two decades, the bacteria causing chancroid and gonorrhoea throughout the world have acquired plasmids that mediate bacterial resistance to penicillins and other antibiotics. This has significantly increased the costs of treatment. There is little prospect that the prevalence of gonorrhoea, chancroid, syphilis and HIV will decrease in the tropics in the near future without a global change in sexual behaviours and practices.