Patterns of HIV infection and disease are changing. HIV will soon enter the top five causes of death worldwide and is now believed to cause more deaths than malaria. Commonwealth countries account for around 60% of prevalent HIV infections worldwide. Around half of all global HIV transmissions are to people under 25 years of age. HIV is lowering life expectancy and reversing gains in child survival in east and central Africa. The incidence and prevalence of HIV infection have increased enormously in southern Africa recently. A more generalised pattern of heterosexual HIV transmission is emerging in parts of South and South East Asia. Injecting drug use and related HIV transmission is increasing in resource-poor countries. Countries where HIV prevalence is low but rising and there are high levels of other STIs offer particular opportunities for early intervention, as it is easier to intervene against HIV when it is entering a country than when it has become established. In countries with weak family and social networks there is inadequate care for the increasing numbers of parentless children. HIV is prejudicing tuberculosis control programme in most African countries and will do the same in Asia. AIDS mortality has fallen in industrialised countries but the prevalence of HIV infection and treatment costs are increasing. Countries that have used multisectoral approaches at an early stage and have had political support for HIV prevention early in their epidemics have been able to limit transmission. Others, intervening later, have been able to reduce transmission. Surveillance methods need to adapt to changing patterns of infection and disease.