Japan has witnessed the rise of STDs, and the increase in the number of HIV cases infected through sexual contact in the last decade. Background of these trends will be the exceptionally high prevalence of paid sex in Japan among developed countries and the diversified unprotected sexual behaviors that have prevailed among general population since 1990s. STDs are also increasing and HIV infection through sexual contact has resumed to increase among other developed countries in the same period of time. Coordinated research among developed countries is becoming increasingly important to clarify the specific and general causes of such phenomena and thus to explore the possibility of coordinated responses toward these global challenges.