This review puts the HIV/AIDS epidemic into perspective against other new and re-emerging diseases that have raged among human populations since the beginning of agriculture around 10,000 years ago, including SARS, bovine spongiform encephalopathy (BSE)/variant Creutzfeldt-Jakob disease (vCJD) and Nipah fever, and old diseases such as tuberculosis and cholera. The authors argue that with a better understanding of how the emergence of such diseases is governed by changes in human ecology – such as movement, environment, living conditions and social interactions – we may be in a better position to anticipate when and where there is a risk of another new disease appearing.