Background Neurobiological studies of the early course of psychoses, such as schizophrenia, allow investigation of pathophysiology without the confounds of illness chronicity and treatment. Aims To review the recent literature on the biology of the early course of psychoses. Method We carried out a critical appraisal of the recent findings in the neurobiology of early psychoses, using structural, functional and neurochemical imaging techniques. Results Brain structural alterations are present early in the illness and may predate symptom onset. Some changes, notably those in frontal and temporal lobes, can progress during the early phases of the illness. Functional and neurochemical brain abnormalities can also be seen in the premorbid and the early phases of the illness. Some, although not all, changes can be trait-like whereas some others might progress during the early years. Conclusions A better understanding of such changes, especially during the critical periods of the prodrome, around the transition to the psychotic phase and during the early phases of the illness is crucial for continued research into preventive intervention strategies.