Approximately 95% of children with autism spectrum disorder (ASD) have at least one common co-occurring condition. Moreover, in the majority of cases, children with ASD who have co-occurring conditions are more likely to be diagnosed with a developmental disorder at younger ages. The prevalence of the 18 most common co-occurring conditions examined in this study varied based on the age of the child. These conditions include: adaptive developmental disability; aggression; anxiety; attention-deficit/hyperactivity disorder (ADHD); congenital conditions including cerebral palsy, encephalopathy, vision impairment and hearing loss; cognitive disability; developmental regression; eating or drinking abnormalities; epilepsy/seizure . . .