1,1,1-Trichloro-2,2'bis(p-chlorophenyl) ethane (DDT) was the first widely used synthetic pesticide and is extremely persistent in both the environment and the human body. The introduction of DDT revolutionised agricultural production and has been credited with the elimination of malaria from the United States and Europe. However, DDT is also known to have had major environmental consequences and has been associated with dramatic declines in many animal populations. Although DDT use has generally been restricted since the early 1970s, exposure to the pesticide remains widespread. In developed countries, slow elimination from the body means a large proportion of the population still have detectable levels of DDT, or its metabolite DDE, in their serum or adipose tissue. In developing countries, the pesticide continues to be used for vector control and a significant proportion of breast-fed babies has daily intakes above recommended levels. This review considers the epidemiological evidence for possible adverse effects of human exposure to DDT. Much of this research is weakened by methodological flaws. However, recent methods in breast cancer research using nested studies in cohorts with stored biological samples have allowed a more rigorous assessment of a putative role for DDT in disease aetiology. While DDT does not appear to play a causative role in breast cancer development, there is suggestive evidence for a role in the aetiology of other conditions such as pancreatic cancer, neuropsychological dysfunction, and reproductive outcomes. Research into these and other conditions would benefit from the same rigorous approaches used in breast cancer research. Until further high quality evidence is available, it is still too early, even 60 years after the introduction of this once ubiquitous chemical, to pass judgement on the role of DDT in a number of common diseases.