Yes. Autism can qualify for the Disability Tax Credit. It is not automatic. The CRA does not approve the DTC because of a diagnosis. It approves it because of the effects of the disability on daily life.
Most autism claims qualify through a marked restriction in a basic activity of daily living — most often speaking, or the mental functions needed for everyday life. A marked restriction means the person is unable to do the activity, or takes an inordinate amount of time to do it, all or substantially all of the time. CRA reads “all or substantially all” as at least 90% of the time, and generally treats “an inordinate amount of time” as at least three times longer than someone of similar age without the impairment.
There is a second, much narrower route for life-sustaining therapy that supports a vital function, needed at least twice a week and averaging at least 14 hours a week. It applies to few autism claims — the marked-restriction route is the usual path.
The impairment also has to be prolonged, meaning it has lasted or is expected to last at least 12 months. Autism is lifelong, so this part is usually straightforward. Your medical practitioner makes the case in Part B of Form T2201, and approval depends on how clearly Part B describes the day-to-day effects rather than on how the diagnosis is worded. If you were already eligible in earlier years, you can ask for adjustments going back up to 10 years.