You may notice, if you know to look for it, that this site refers to ‘autistic people’, rather than ‘people with autism’.  This is a deliberate choice, although it runs counter to the standard practice in health, counselling and educational settings.

Person-first language means using a term like “person with autism”.  Most health and social science professionals have been taught that they should always use person-first language because it acknowledges personhood primarily, and separates the person from their [disability / illness / undesirable aspect].  It suggests that there is a person hiding within the autism, who should be acknowledged over and above the fact of the autism diagnosis.  Some adults with autism also prefer this terminology for themselves.

Identity-first language means using something like “autistic person”.  Many – perhaps most – autistic adults prefer identity first language.  Autism is not something we can be separated from (or – in fact – would wish to be separated from).  It is fundamental and inherent, and we do not perceive it as an undesirable aspect of ourselves.  There are certainly aspects of autism that can be distressing and uncomfortable, and most of us would love to minimise the impact of these on our functioning.  However, there are also many aspects of autism that are incredible and positive.

There is a lot of debate about Person-first language in the autism community.  My clear personal preference is for identity first language, and I consider the idea that people may need to use a language formula to remember that there is a person in front of them to be something of a concern.  However, I don’t consider there to be a clearly right or wrong language choice; both forms are in use in the autistic community.
But it is not ever acceptable to criticise the choice of autistic people – to choose for them, or tell them that their language is wrong.  Self-identification is a powerful thing.

A much more sensitive and sensible approach is “Person-centred language”, which means hearing the terms used by the person themselves, and using them.  If you need to check with them on preferred language, do so.

There are a number of excellent blogs on this topic, if you’re seeking more information.

http://autisticadvocacy.org/about-asan/identity-first-language/
http://www.autistichoya.com/2011/11/identity-and-hypocrisy-second-argument.html
http://autismmythbusters.com/general-public/autistic-vs-people-with-autism/jim-sinclair-why-i-dislike-person-first-language/
And more, available here: https://www.identityfirstautistic.org/links