We provide a systematic review of epidemiological surveys of autistic condition and pervasive developmental disorders (PDDs) worldwide. A secondary purpose was to think about the feasible influence of geographic, cultural/ethnic, and socioeconomic elements on prevalence estimates and on medical presentation of PDD. Dependent on the proof reviewed, the median of prevalence estimates of autism spectrum disorders was 62/10 000. While present estimates are variable, the evidence reviewed does not assistance variances in PDD prevalence by geographic area nor of a robust effect of ethnic/cultural or socioeconomic variables. Even so, electrical power to detect this sort of consequences is severely limited in current knowledge sets, specifically in reduced-revenue nations. Whilst it is distinct that prevalence estimates have increased above time and these differ in diverse neighboring and distant regions, these findings most most likely stand for broadening of the diagnostic concets, diagnostic changing from other developmental disabilities to PDD, services availability, and awareness of autistic spectrum issues in the two the lay and skilled community. The lack of proof from the majority of the world’s population indicates a essential need for more investigation and ability developing in lower- and middle-revenue nations around the world. Autism Res 2012, ••: ••–••. © 2012 Global Society for Autism Investigation, Wiley Periodicals, Inc.