Does childhood ADD go away?

I was diagnosed with ADD as a child and took Ritalin for a very short period of time because one of my family members was in denial of my issues. I never really thought of it again in my life until recently. Light bulbs seems to be going off. I am 26 now and every attempt at doing anything studious is difficult for me, I cannot seem to concentrate. I love to read and that is hard most of the time. I love to write and that is extremely hard to sit and do. I am very forgetful and unorganized and the list goes on. I was just curious does childhood ADD go away or is it a life long illness? Do adults with ADD or ADHD develop it in their adulthood? If not do I have to be diagnosed all over again?