One does not need to see a doctor before applying for SSI. However, it will be very difficult to prove a disability without ongoing treatment. The Social Security Administration will most likely provide an examination after the application, if there is not enough medical information available at the the time of the application. However, if your son is denied disability at the initial level, they will not provide treatment nor another exam. There is no good solution to this problem. Some counties and cities do provide a basic level of care for people who have applied for SSI. He can also apply for Medicaid, though typically that is denied until the SSI is granted. Though it can be very difficult, perhaps the family can pay for care on a somewhat continuous basis until the case is resolved.