Do you capitalize obsessive compulsive disorder?

Answer 1

Assuming you mean when you write or type it out, no.

Only capitalize the name of a disease or condition if it includes a proper noun (names, titles, etc.) such as "Alzheimer's disease" (notice that "disease" still isn't capitalized because it's not a proper noun).

P.S. if you want to get finicky about it, OCD spelled out should be: obsessive-compulsive disorder.

P.P.S. if you're at all interested in knowing more about this kind of grammar and punctuation stuff, check these links out:

http://www.arts.uottawa.ca/writcent/hypergrammar/partsp.html

http://www.grammarbook.com/punctuation/capital.asp

Hope that helped!