The DSM IV-TR also includes "Mental Retardation" as a diagnosis. Supporters of this population prefer "developmentally disabled," but "mentally retarded" is technically correct. And generally accurate - referring to delays in attaining developmental milestones due to intellectual impairment. Intellectually impaired is another accepted term.

Whe I was working with this population, I heard some of the clients using "retarded" as an insult, without understanding what it meant - often they were referring to some celebrity that they or another client were obsessed with. I also had one client come into my office one day (she had a routine, where every day she sat down by my desk for about 5-10 minutes and usually told me she was going to take a train to Alaska for vacation), anyway, one day she came in and said, "do you know that I am mentally retarded?" I just pointed out the many things that she could do well, and that she genuinely enjoyed life and did things like anyone else would, and that was what counts. She was very matter of fact and not upset - just learning a new word.