In this selective review of the literature, we present the most recent prevalence estimates for autism spectrum disorder (ASD) and discuss the limitations and challenges in interpreting changes in prevalence estimates over time. Increases in ASD prevalence estimates cannot currently be attributed to a true increase in the incidence of ASD due to multiple confounding factors. These include broader diagnostic criteria and a greater awareness of ASD. The current average prevalence of ASD is approximately 66⁄10,000, which translates to approximately 1 in 152 children a ected, with males consistently outnumbering females by about 5:1. Several recent studies have reported higher estimates ranging from 147 (one in 68) to 264 (one in 38) per 10,000. This is in sharp contrast to the gures of about 1-5⁄10,000 quoted in earlier studies that used a narrow de nition of autistic disorder and were not inclusive of all disorders falling onto the autism spectrum. It remains to be seen how changes to diagnostic criteria introduced in the DSM-5 will impact estimates of ASD prevalence.