How long does it take for autism to be completely gone?

There is no cure: There is no cure for autsim so it will never be "gone", rather is it a part of who you are.

Never: Autism is never completely gone. High functioning patients are more able to mix in mainstream society over time than lower functioning ones. It's very individual. Never give up hope. Work hard to help your autistic child to communicate and find success in an area of interest.

Not Ever Totally: There are many degrees of autism. Although total cure is unknown, with proper, proven therapy, there can be huge improvement.So great, that some are able to function almost normally in society. Unfortunately, there are more severe cases that will never do well. The earlier the diagnosis, the greater chances of improvement.

Better, not curable: The current thinking of autism and ASD is that it is a developmental disorder that persists for life. That said, with intensive early therapy and social skills training there are reports of kids, especially in the milder PDD or Aspergers end of the spectrum that seem to " grow out of " the disorder.

Autism is life long: Autism is a life long condition. there are isolated reports of children growling out of autism, but these are likely who never had autism and were misdiagnosed. Some children with Asperger's disorder (a condition considered autism but I do not believe so), may as they mature, appear more like children with non verbal learning disability.