Up to 31 December 1987, 1227 cases meeting the World Health Organization Centers for Disease Control (U.S.A.) (WHO/CDC) definition of the acquired immune deficiency syndrome (AIDS) were reported in the U.K., of which 54 were in persons who came to the U.K. for diagnosis and treatment and 1173 in U.K. residents. In the same period there were 8003 laboratory reports of human immunodeficiency virus (HIV) antibody-positive tests. The upward trend in the number of AIDS cases by quarter changed in the last quarter of 1987, when there were only 163 new reports. Predictions were revised so that 1450 new reports are expected in 1988. During a temporary increase in the number of tests performed in the first quarter of 1987, associated with a publicity campaign, the testing threshold for members of the homosexual/bisexual male risk group fell. The proportion of HIV antibody positive homosexual/bisexual men who were ill when tested in 1985 was between 50 and 73 each quarter; after 1985, this proportion has varied between 38 and 49%. The concentration of AIDS cases in the four Thames regions was marked, whereas HIV antibody-positive reports were more widely distributed. Since 1985, the proportion of the total HIV antibody-positive reports from the Thames-regions increased from less than a half to two-thirds. Among HIV antibody-positive women, over half were IV drug abusers and over two-thirds were in the age group 15-29 years. There were 19 cases of AIDS in children aged 14 years or less, eight of which were in visitors to the U.K. Of the 11 cases in U.K. residents, seven were in children of mothers known to have, or to be at risk of, HIV infection. The distribution of the 253 HIV antibody-positive reports in children was different; most were in haemophiliacs or blood/components recipients aged 5-14 years. Most mothers who have infected their children in utero were either IV drug abusers or sexual partners of IV drug abusers. Lymphoid interstitial pneumonia was the commonest indicator disease at the time of diagnosing AIDS in children. The mean age at diagnosis was 2 years 4 months for those infected in utero and 3 years 7 months for those otherwise infected. Between 1985 and 1987 there were marked increases of children with AIDS, of HIV antibody-positive children of infected/at-risk mothers and of reported HIV infections in women of child-bearing age. In the near future it is likely that many more pregnancies, particularly in Scotland, will be complicated by HIV infection.