You can always apply for SSI, but whether he gets it or not depends not so much on the diagnosis but by how disabling the condition is in interfering in the ability to sustain gainful employment, by how incapacitating it is in the academic arena if he is still in school, or how deficient adaptive behaviors or activities of daily living are. I do many evaluations for Social Security, and I have three adopted children with ASD, one mild, one moderate, and one severe. The mild and moderate ones are identical twins. The moderate and severe ones were approved for SSI, the mild one was denied benefits even though her twin was approved. So it depends on capabilities and not necessarily diagnosis. Apply anyway and SSA will determine if he qualifies. The test results from the psychiatrist and his or her opinion can be used to to aid in their decision or they may send him to another independent consultant for another opinion. You can have ADHD and get SSI, or have ADHD and function normally from being on Adderall and therefore not be granted SSI because you're not disabled. See? It's not entirely about a diagnosis, but by the degree of disability. Even a high functioning ASD like Aspergers Disorder can still get SSI if it interferes significantly with schoolwork, socializing or keeping a job. If you don't like SSA's denial, you can always appeal their decision and even hire a lawyer to advocate your case, but you better be able to prove how disabled he is by SSA criteria.