Immigration to Spain has greatly increased since 1995. Currently, more than 4 million foreigners are resident in the country. The immigration process increases vulnerability. The most common route of HIV infection in the immigrant population and ethnic minorities is heterosexual transmission. The number of people living with HIV worldwide (39.5 million people in 2006) and the number of those dying from AIDS continues to increase. In 2006, there were an estimated 30,000 people living with HIV/AIDS in Spain. The number of cases of AIDS in immigrants has risen in the last few years. AIDS in immigrants from any country, and especially in those from sub-Saharan Africa, is associated with a greater frequency of tuberculosis disease. Knowledge of opportunistic pathogens with tropical distribution is required for a correct differential diagnosis. Throughout the European Union, the number of AIDS cases has progressively decreased since the introduction of highly effective anti- HIV treatment, but this decrease has been significantly lower in immigrants. The difference may be due to lower access to health systems caused by administrative, legal, cultural and linguistic barriers.