The HIV/AIDS pandemic has devastated many countries, reversing national development, widening the gap between rich and poor people, and pushing already stigmatised groups closer to the margins of society.1 It has killed millions of people, decimated families and communities, and adversely affected the lives of hundreds of millions. AIDS stands to kill more than half the young adults in the most severely affected countries.1

By the end of 2001 an estimated 65 million people worldwide had been infected with HIV—25 million had died and 40 million were living with HIV or AIDS, most of whom have no access to the lifesaving drugs available in industrialised countries.1 Countries in sub-Saharan Africa and South and South East Asia are the worst affected (fig 1).

The pandemic continues its relentless spread—about 14 000 people are infected each day. This article describes the impact on health and the economic and social impact of the HIV/AIDS pandemic in poor countries, discusses the many factors that promote the heterosexual transmission of HIV, highlights successes around the world in preventing infection, and outlines some of the challenges for the future.