The notion that subtle cognitive, emotional, behavioral, and functional deviations from norms are present in many individuals several years before a formal diagnosis of schizophrenia has been around for almost a century. This notion has been at the base of the developmental hypothesis of schizophrenia and has been the impetus for the use of cognition as an endophenotype for studying the illness. The recent enthusiasm for prodromal research derives from two unrelated and controversial claims: that short duration of untreated psychosis is associated with better prognosis and that novel antipsychotic drugs have a better safety profile, supposedly enabling early intervention at a relatively lower risk of side effects to the patient.

At the current level of knowledge, the risk-benefit assessment of prodromal interventions turns out to be an almost unsolvable conundrum. On one hand, the age of onset of psychosis and schizophrenia, early and mid-ado-lescence, coincides with the age at which life-long social and vocational characteristics are shaped. Any intervention that could produce even minimal delay in onset of active psychosis or ameliorate its early course might have a life-long impact. Therefore, the idea of prodromal intervention cannot be easily dismissed. On the other hand, in absence of accurate markers for imminent psychosis and strong data indicating that treatment during the prodromal phase is effective, exposing adolescents to the stigma associated with the illness and the adverse effects of antipsychotics has raised serious hesitations among many researchers and clinicians.

In treating schizophrenia there has been a shift in focus, with more attention being paid to early intervention based on the notion that effective treatment at this point can improve outcome. Most of this work has centred on pharmacotherapeutic interventions during the first psychotic break. More recently, attention has turned to the potential value of intervening even earlier, that is during the so-called “prodrome” that has been identified as predating the first psychotic break by as much as 4–5 years. We now have a limited number of published reports addressing this topic and these are reviewed here.

Accurate identification of individuals in the earliest symptomatic stages of psychosis offers new hope for developing more effective treatment strategies. Recently, research clinics have been set up to identify and possibly treat individuals who are seen as being at ultra-high risk of developing a psychotic disorder. This article reviews and describes measures that are currently being used and further developed in order to determine both the diagnostic criteria for the prodromal state and the severity of these putatively prodromal symptoms.

Research has shown that many of the long-term deficits that are observable in schizophrenia populations are present prior to the emergence of psychotic symptoms. Recent research suggests schizophrenia has a “prodromal” period, whereby significant changes from premorbid functioning can be observed. Accurate classification of this period could have far-reaching implications for schizophrenia prevention. This article aims to provide an indepth evaluation of the perceived benefits of vulnerability marker research in this unique phase. It is hoped that identification of such markers may improve the predictive potency of prodromal criteria, and perhaps pave the way for future screening and primary prevention strategies.