So where do you start when ask this question? With your life history, how about why you want be a veterinarian? Any current students want to share with us how you answered the question.
Hahahahahaha. I went into my interview all gloaty and happy knowing I wouldn't be asked that question because MN did "behavioral" interviews....
.... and then the very first thing out of their mouths after the friendly "have a seat" and whatnot chit-chat was: "So... tell us a little about yourself."
I only bring this up to prepare people who think that they've heard about the way a particular school does interviews and think that question may not come up. Don't be unprepared for it like I was. Or, apparently, like EG.
(I don't think I flubbed it quite like that, EG, but I'm sure I hemmed and hawed a bit.)
As far as an answer ... I opted for an abbreviated timeline of my adult life (since I'm a non-traditional), focusing on elements that I thought highlighted why I would uniquely be a valuable addition to the school. The reason for timelining it is that it keeps your thoughts on track and helps prevent bouncing around (which confuses them and gives the impression that yer thoughts aren't organized).
I agree with what racccjlm said about not covering material in your application, but with a couple caveats: First, schools do 'closed book' or 'open book' interviews. In a 'closed book', the interviewers won't have looked over your application, so there's no harm covering that ground again if it's useful. Research your particular school to find out how they do it. I just plain outright asked at the beginning of my interview - don't be shy about doing that. It's not a state secret. I tried to be tactful about how I asked - something like "So I don't cover ground you've already read about, can you tell me if you've reviewed my application?" Second, having SOME overlap with your application is good, because it promotes the image of a coherent, unified application where the strong points are repeatedly emphasized. There's a balance between over-repetition and leaving them wondering why you didn't include something on your PS or whatever.