Globalization and its associated international migrations facilitate the spread of infectious diseases. This article reports trends in and discusses the relation between international migration and HIV infection in Japan. The authors analyze relevant literature, drawing on government and other sources. Among foreigners in Japan, there were 27.0 reported HIV and 9.3 reported AIDS cases per million in 1990, and 52.9 HIV and 38.8 AIDS cases per million in 2000. These rates were initially 45 to 90 times the population prevalence of HIV and AIDS among Japanese, but are now only 10 to 20 times the prevalence among Japanese, as HIV becomes an increasing problem for the Japanese population. HIV-infected foreigners who are uninsured are at a disadvantage for diagnosis, counseling, and treatment compared with insured persons, and at a significantly higher risk for low CD4 counts. For all sections of Japan's population, counseling and testing are inadequate, and surveillance of behavioral risk, infection, and disease is limited. International migrants are at increased risk for HIV transmission and at a disadvantage for care and treatment. Japan needs both to develop policies that assist migrants and to respond to the growing threat among its nonmigrant population.