Epidemiologic trends of STD are strikingly different in various parts of the world. In Northern and Western Europe there has been a spectacular decline in the incidence of STD, particularly gonorrhea and syphilis. It is probably due to a combination of an early initiation of sex education at school, behavior change, condom promotion, and the wide availability of STD treatment. The situation in North America is far more complex, with geographic areas and large population groups having low levels of STD and others continuing to experience an epidemic of STD, particularly inner-city minority populations in the United States. In developing countries both the prevalence and incidence of STD are still very high and STDs are a major public health problem making up the second cause of healthy life lost in women of 15 and 45 years of age after maternal morbidity and mortality. "Business as usual" is clearly not acceptable any longer. A better understanding of the determinants of STD epidemiology is essential for a more effective approach to STD control as well as recognizing the limitations of each single intervention, be it medical or behavioral. The major challenges are to mobilize political commitment and funds, and to transfer small scale interventions into large scale public health programs, and to apply the right mix of approaches, including medical, behavioral, societal interventions.