[bazillion]

It's very important that everything medical before and during your career is documented. First off, a lot of the physical and mental stress down the road can exacerbate previous conditions and lead to more major problems. Secondly, everything that occurs and is documented in your military health record can be treated for free by any VA medical facility for the rest of your life, even if you don't have health insurance.

That being said, certain common diagnoses will preclude you from entering service: ADD/ADHD, bi-polar disorder, bad knees, fibromyalgia, among other things. Obesity is kind of a no-brainer thing -- there's a maximum body fat percentage and height/weight ratio.

If it's in your health record right now, then it should definitely be declared, in my opinion. You'd only be doing yourself a disservice later on by not doing so.