Hi just my 2 cents . . . My son was diagnosed with ODD and ADHD when he was 3 1/2. I learned a lot of good parenting techniques to deal with defiant behavior from books like, "Your Defiant Child" by Russell Barkley. It helped us tremendously. We tried to avoid medication, but by 4 years old, we were willing to give it a try. He now takes Adderall every day, and with that combined with learning how to parent him better he's doing really really well. Don't get me wrong, we still have really bad days, but for the most part, he's doing great. I too was skeptical that a little 3 1/2 year old could be diagnosed correctly, and for a long time I didn't believe the diagnosis. But, guess what? They were right! He does have ADHD, and now that I know how to treat it, he has a much better life than he would have if I had stayed in denial. I have a very close friend who has a little boy with Asperger's Syndrome, and he was also diagnosed at a very young age (3). With the diagnosis, his parents were able to help him with medication and with different parenting techniques, and he's now in a special kindergarten class in the public school that's only for kids on the autism spectrum, and he's doing awesome. If they hadn't gotten an early diagnosis, I really don't think he'd be doing so well. Anyway, the point of all of this is that I do think that its possible to get the right diagnosis at a young age. You just have to find the right person/people to do the diagnosis. It's tough. It can be very difficult for the family if you get the wrong diagnosis, and treat your child with the wrong medication or techniques thinking that he has something he doesn't. But if you do find a great diagnostitian, and get it right, I personally believe that it can make all the difference in the world. Anyhow, good luck. And you're off to the right start just finding this website.