Background: Pervasive developmental disorders (PDDs) were originally conceptualised as a form of ("infantile") psychosis. Recently, the disorders have been viewed as separate constructs. However, there is evidence of overlapping psychopathology, pathophysiology, and occurrence of the two syndromes. Methods: A historical overview is provided. A systematic search strategy was then used to identify literature relating to the co-occurrence of PDD and nonaffective psychosis. Results: The methodology and estimated rates of psychosis occurring in PDD varied dramatically, and few conclusions could be drawn due to the level of heterogeneity and selection bias in the populations studied. However, there were indications from the literature that rates of comorbid PDD were elevated in adolescents affected by juvenile-onset psychosis but the methodology was insufficiently robust to estimate a pooled prevalence. Conclusions: There is some evidence for elevated rates of comorbid PDD in individuals with childhood-onset psychosis. Further work is needed in order to understand the potential mechanisms underlying such co-occurrence and how such affected individuals can be best supported. (Contains 2 tables.)