AIDS epidemic began about 15 years ago; since then, the number of new cases have increased over time. By the end of 1994, 1,025,073 AIDS cases had been reported to the WHO, with a 20% increase in the number of cases since December 1993. As is now evident that the majority of cases occur in developing countries, under-diagnosis, under-reporting and delays in reporting explain the big difference existing between reported and estimated AIDS cases, giving a 4.5 million cumulative AIDS cases worldwide, as of late 1994. In the industrialized countries, the spread of HIV infection began in the late 1970's or early 1980's among homosexual men and IVDU's. Heterosexual transmission was, at first, very limited, though recent data has shown an increase in its diffusion. On the contrary, in Sub-Saharan Africa and the Caribbean, transmission was almost exclusively heterosexual. High rates of infection among young women led to a corresponding increase of perinatal transmission, infecting more than 1.5 million children since the beginning of the pandemic. The estimated number of HIV infections worldwide, as of late 1994, is of 17 millions. Thus, even if some evidence indicates a possible decline of the pandemic in industrialized countries over the next few years, probably because heterosexual transmission was less common, developing countries appear to present an increasing number of HIV infections in young people and, consequently, in children. The real impact of such an epidemic is stressed by the fact that HIV is becoming the leading cause of death among, young people, both in industrialized and developing countries.(ABSTRACT TRUNCATED AT 250 WORDS)