If he is your qualifying dependent except for the joint income test or gross income test than you can claim medical expenses that you paid for him even if he is not claimed as dependent on your tax return.
To be claimed as a qualifying (dependent)relative, the person must meet five criteria:Gross Income - The dependent earns less than $3,400 (for 2007) in income during the year,Total Support - You provide more than half of the dependent's total support during the year,Relationship - You are related to the dependent in certain ways,
To meet the relationship test, the dependent must either
Joint Return - If the dependent is married, the dependent cannot file a joint return with his or her spouse.
Citizenship - The dependent must be a citizen or resident alien of the United States, Canada, or Mexico
Let me know if you have any question.
Please note: This advice is provided with the understanding that all the relevant facts have been provided by you. Any change in facts might affect the advice given and hence may not be relied on in such cases. Nothing contained in this reply was intended or written to be used, can be used by any taxpayer, or may be relied upon or used by any taxpayer for the purposes of avoiding penalties that may be imposed on the taxpayer under the Internal Revenue Code of 1986, as amended.