SummaryPsychotic symptoms are common in the general population. There is evidence for common mechanisms underlying such symptoms in health and illness (such as the functional role of mesocorticostriatal circuitry in error-dependent learning) and differentiating factors (relating to non-psychotic features of psychotic illness and to social and emotional aspects of psychotic symptoms). Clinicians should be aware that psychotic symptoms in young people are more often associated with common mental disorders such as depression and anxiety than with severe psychotic illness.