Graphs have been used in attempts to show a relationship between the measles, mumps and rubella virus (MMR) vaccine and autism. We examine the topic of graphical representation of data in general, and one of these graphs in particular: the one that appeared in a 1999 letter to The Lancet. That graph combined data from England and from California, USA. The author alleged that this graph illustrated a rise in autism rates linked to the use of the MMR vaccine. By examining the presentation closely, we are able to show how this graph misrepresented the data used. We give advice for both authors and publishers in the use of such graphical treatments of data.