I was wondering - if I outscored the GMAT average at my target school by almost 100 points, would this be a problem?

I have applied for the MBA at Duke, because of its Health Sector Management program. I took the GMAT, and at the time I realized that I did quite well (790) - but now that I look at the class profiles, it turns out that it's much higher than the typical cohort.

Is it possible that they would ding an applicant because of this?

No, I think that's unlikely. Certainly they would look to see if you were a rounded person, because very high scores can be a sign of one-sided personal development. Other things being equal, a higher GMAT is better.

PS Also review http://www.find-mba.com/specializations/15/health-care-pharmaceuticals-biotechnology

What does the rest of your profile look like? In particular, how much work experience do you have?

Duke is great and all, but you may want to aim higher: a top-tier school with a health specialization (Columbia has a healthcare management concentration; as does Wharton) might be worth considering.

Oh, that's good to know. I was pretty set on Duke because I live nearby, but if what you are saying is true, maybe I should take Columbia seriously. In terms of my profile, I have 4 years of work experience, mainly for one HMO, mostly in an accounting role. I have fairly good undergraduate grades, but no real extra curricular activities to speak of.