First, if you are an adult and weren't diagnosed as a child, you will find it VERY difficult. As a child you have resources in schools, in public health, etc--if you are anywhere on the autism spectrum, they will catch you. But if you are an adult, especially if you are a smart adult who functions very well in life, you easily slip through the cracks.
This article pinpoints the problems with getting diagnosed as an adult pretty well:
"Adults with ASDs are more likely to be recognized and supported if they also have severe intellectual disability; those with higher levels of functioning tend to be overlooked in the community."Well, exactly.
You also find interesting bits of information like this. The curious part is that men have a higher occurrence of ASD then women. This strikes me as interesting, and in another post I will research it more thoroughly and confirm or disprove this article.
The best advice I have seen for an adult who thinks they might be on the Spectrum is here, and frankly, I'd rather find a more authoritative source, but I haven't found it yet.
Most importantly, it is good to have knowledge and information on your side, to look at blogs and other sites that have discussions with people on the Spectrum (Rethinking Autism is a good place to start), and to really have your ducks in a row before you approach a professional. I was diagnosed incorrectly with Bipolar disorder several times before they got it right. The clue? If they have to work really hard to make you 'fit' with the DSM standards for having Bipolar disorder, you probably aren't Bipolar. First I was Bipolar II, then I was Cyclothymic, then I had Bipoloar Spectrum disorder, and on and on it went. I finally sat down with my Psychiatrist and told him as odd as it is for me to tell you my diagnosis is wrong as you are the professional and I am not, I have done my research and I am very self aware, and I am NOT Bipolar. I have Autism Spectrum Disorder. I then used the DSM other materials to lay out all the reasons I wasn't bipolar, and all the reasons I did have ASD.
He looked at me for a minute without speaking, then said, you are absolutely right. You have Autism Spectrum Disorder.
It was a proud moment.
Good luck to all who are still seeking to find the truth!