I am making the assumption here that your son is not "permanently and totally disabled" as defined by the IRS. Opus 17 is making the same assumption. If our assumption is true, then you cannot claim your son as a dependent. If we're wrong, then you probably can claim him as a dependent.
We are also assuming that he lived with you for more than half the year. If not, that could change the picture if he is considered "permanently and totally disabled."
Whether or not you can claim your son as a dependent affects whether or not he has to file a tax return.
