Approximately 20.1% of adults, aged 18 to 27, with autism spectrum disorder (ASD) also have an anxiety disorder, compared to just 8.7% of adults without ASD. For adults with ASD and anxiety disorder, their biological siblings without ASD also were more likely to receive an anxiety diagnosis (a 1.50 risk ratio) compared to the general population (a 1.37 risk ratio). The greatest risk for co-occurring autism and anxiety disorder occurs in those without intellectual disability, at 23.1%. Additional findings include: About 20.1% of adults with ASD have an anxiety disorder, compared . . .