Parental reports on the prevalence of co-occurring intellectual disability among children with autism spectrum disorders

Limited evidence suggests that the prevalence of mental retardation (MR) – now called “intellectual disability” (ID) – in ASD ranges between 25.8% and 58.5%, with co-occurrence in 66–70% of children who meet strict criteria for autism. However, parents and professionals differ significantly in their understanding of or opinions about intellectual functioning among children with ASD. The current study analyzed archival data to calculate the prevalence of parent-reported MR among children with ASD (N = 498). Collectively, 9.2% of families affirmed MR; when analyzed by type of ASD, the rates for those with autism and PDD-NOS were 12.6% and 7.3%, respectively. A variety of explanations for these low rates are posited alongside implications for clinical practice and families’ receipt of services.