Objective: The cognitive and motivational impairments observed in psychotic disorders may reflect early developmental alterations that, when combined with later environmental exposures, may drive the onset of positive psychotic symptoms. The epidemiological predictions of this model were tested. Method: A longitudinal prospective cohort study (the Early Developmental Stages of Psychopathology Study) was conducted with a representative general population sample of adolescents and young adults from Munich (N=3,021), who were 14-24 years of age at baseline. Sociodemographic factors, environmental exposures, and measures of psychopathology and associated clinical relevance were assessed across three waves, covering a period of up to 10 years, by clinical psychologists using the Composite International Diagnostic Interview. Results: Both negative/disorganized and positive psychotic symptoms were frequent (5-year cumulative prevalence rates of around 12%) and occurred in combination more often than predicted by chance. Negative/disorganized symptoms revealed a pattern of sociodemographic associations indicative of developmental impairment, whereas the positive symptoms were associated with environmental exposures such as trauma, cannabis use, and urbanicity. Negative/disorganized symptoms predicted positive symptoms over time, and co-occurrence of positive and negative/disorganized symptoms was predictive of clinical relevance in terms of secondary functional impairment and help-seeking behavior. Conclusions: The results suggest that the negative/disorganized features associated with psychotic disorder are distributed at the population level and drive the ontogenesis of positive psychotic experiences after exposure to environmental risks, increasing the likelihood of impairment and need for care.