In the past decade there has been great interest in studying a group of young people at ultra high risk for psychotic illnesses such as schizophrenia. These people are at hugely increased risk because of a combination of symptoms and personal or family history, and indeed around 20% of them develop psychosis within 12 months of being identified. It is now clear that there are differences in the brains of these at-risk cases when compared to similar participants not at risk, and that these brain differences get greater with the onset of psychotic illness. What is still not known is when these changes occur during the progression. For example, it could be that the changes come before (and somehow cause) the increase in symptoms, which would imply that trying to prevent those brain changes could prevent the illness.