[smilesnd]

Autism is a neurodevelopmental disorder characterized by impaired social interaction, verbal and non-verbal communication, and restricted and repetitive behavior.

A mental disorder, also called a mental illness[1] or psychiatric disorder, is a diagnosis by a mental health professional of a behavioral or mental pattern that may cause suffering or a poor ability to function in life. Such features may be persistent, relapsing and remitting, or occur as a single episode. Many disorders have been described, with signs and symptoms that vary widely between specific disorders.

Hence autism does fall into the category of mental illness. Maybe psychiatric disorder would be a better term, but pears to pears at this point.