It is well accepted that most serious psychiatric conditions begin in adolescence and are characterized by initial symptoms that predate the full manifestation of illness. This early period often consists of nonspecific symptoms, making accurate detection difficult. Classification as "prodromal" is only possible retrospectively, after a patient has developed positive psychotic symptoms. To monitor these patients prospectively, we must identify and follow patients who are at risk for psychosis, understanding that this group may also include false positives who do not go on to develop psychotic illness. Improving detection of at-risk individuals gives us an opportunity to intervene earlier in the course of the disorder, creating a window of opportunity to improve outcome and decrease overall burden of illness.