This chapter presents data from the latest surveys and demonstrates the underlying trend of dramatically increased diagnosis of autism in Europe and the USA since the 1990s, and assesses its limitations. Taken together, the figures and data illustrate that the time trend in autism diagnosis and identification is upward. All the datasets give a similar picture, despite their various limits, fluctuations and problems. The chapter then puts forward competing explanations, either that the rise is solely an ‘artefact’ of changing diagnostic practice, the expanding boundaries of the diagnostic category of autism and other cultural changes, as many epidemiologists, clinicians and researchers believe, or that in addition there is a ‘real’ increase in the proportion of children who display traits characteristic of autism. The chapter reviews who is saying what in this arena and how this can lead to differing interpretations of the same data. The rise in autism is a case in which selective interpretation of data, selective publication and the political context in which scientific institutions sit have shaped scientific discourse.