My son was misdiagnosed with autism (Asperger's) when he was 9. His actual issue was being HGish with dyslexia. The person who diagnosed Asperger's thought his interests were odd. He was "undiagnosed" at age 10.

He is now 24 and very obviously not autistic.

There is an interesting discussion of this issue in the book Misdiagnosis by Webb and colleagues.