This study examined the hypothesis that developmental expression of psychometric risk in the form of subclinical psychotic experiences in the general population is usually transitory but in some instances may become abnormally persistent and progress to a clinical psychotic state. A prospective cohort study was conducted in a general population sample of 845 adolescents, aged 14-17 years, in Munich, Germany (Early Developmental Stages of Psychopathology Study). Expression of psychosis was assessed 4 times (T0-T3) over a period of 8.4 years. Transition from subclinical psychosis at T0-T2 to clinical psychosis in terms of impairment at T3 was examined as a function of the level of prior persistence of subclinical psychosis (present never, once, twice, or thrice). The more the subclinical psychosis persisted over the period T0-T2, the greater the risk of transition to clinical psychosis at T3 in a dose-response fashion (subclinical psychosis expression once over T0-T2: odds ratio [OR] = 1.5 [95% confidence interval {CI} = 0.6-3.7], posttest probability [PP] = 5%; twice: OR = 5.0 [95% CI = 1.6-15.9], PP = 16%; at all 3 measurements: OR = 9.9 [95% CI = 2.5-39.8], PP = 27%). Of all clinical psychosis at T3, more than a third (38.3%) was preceded by subclinical psychotic experiences at least once and a fifth (19.6%) at least twice. Consequently, a significant proportion of psychotic disorder may be conceptualized as the rare poor outcome of a common developmental phenotype characterized by persistence of psychometrically detectable subclinical psychotic experiences. This may be summarized descriptively as a psychosis proneness-persistence-impairment model of psychotic disorder.