If you were a woman, black, or an amputee, your interviewer would immediately know what was up with that, with no confusion and no need to ask. If you were gay it would be none of their business to know and wouldn't affect your interview in the slightest. ​ Explaining that you stutter is totally optional and I don't have an opinion either way as to whether you should or shouldn't do that, but I think the reason people do it is they want to save their interviewer from wondering what's going on. Awareness of stuttering is not that high and people aren't necessarily always going to instantly know and understand what it is. ​ Edit: Also to point out, you really don't want your interviewer to be sitting there thinking "what is going on with this, what does it mean and how should I respond to it" because then they're not listening to what you're actually saying. Your time in the interview is precious, so it's sensible to do whatever you can to focus their attention on your skills and accomplishments and suitability for the job role. ​ Edit #2: Probably a lot depends on how your fluency actually is during the interview? If you're mostly fluent, your interviewer is probably not going to think about your speech at all and there's no need to complicate matters by mentioning it. On the other hand if you take a full minute to say hello, they're bound to be confused.