In 1992, HIV infection in children is essentially due to vertical or perinatal transmission, i.e. from the mother to the fetus and neonates. This is a particularly serious public-health problem in Africa where the percentage of infected women of child bearing age is as high as 20% in some suburban areas. During the last few years, three important points have been established. (i) In Europe and North America, the rate of perinatal transmission is between 15 and 25% and appears to have remained relatively stable with time in various prospective cohorts. (ii) Considerable efforts have been directed at defining the optimal methods for early diagnosis of HIV infection in the infants. At present viral cultures and gene amplification of HIV DNA by polymerase chain reaction are the most promising procedures for early diagnosis within the first 6 months of life. (iii) Finally, the course of the disease in the infected infant has been well characterised, it takes two main forms--that of an early and severe disease or that of a slowly progressive infection: In addition, follow-up is now sufficient to confirm that children with negative tests at 15 months are indeed uninfected. However, knowledge is lacking in a number of essential areas. These include the exact timing of transmission (in utero, during delivery or post-partum), the relative frequency of transmission during each period, the mechanism(s) involved (particularly the role of the placenta), and, finally, the influence of maternal, fetal and viral factors. Answers must be found rapidly in order to develop preventive therapy, to identify women who may have an increased risk of transmitting the virus, to develop a reliable antenatal diagnostic test and, finally, to be in a better position to inform HIV-seropositive women of the relative risks.