Parents attending thesis defense? My wife is defending her thesis soon, and in her department, defenses are open to the public. I will be there along with several of her friends/colleagues. Her mom also wants to come to the defense. In terms of her committee's perception, I could see this being viewed as weird or maybe unprofessional. Then again, it could be harmless, and her mom really wants to come. I also happen to be in the business of trying to keep my mother-in-law happy :)

How would this look from the perspective of her committee? Do parents ever come to defenses? I haven't really heard of this before. I want my wife to have the best chance at passing her defense, but I also don't want to come across as a grouchy husband that appears to be saying, "Your mom can't be here."

This is a Nutritional Sciences department in the United States. It is a somewhat unique situation in that students typically start a dietetic internship a week or so after defending the thesis. The internship takes months to plan for the student since it involves organization with preceptors at multiple locations.

At our university, there are three possible results from a defense: passing, passing with modifications, or failing. Passing with heavy modifications could result in a delay (of a month or more) in starting the internship. This recently happened to another student.

My wife asked me to ask this question here as she wants to focus on getting prepared for the defense. She initially asked for my gut feeling on her mother attending, and I had never heard of this before, nor had she. The defense is coming up very soon ;) and she did not feel comfortable asking her advisor a question like this so late. Also her advisor is not the most responsive to email so she might not even hear in time (I know that this will probably invoke statements that she should get over it or that she should not have picked this advisor, but this is not the point of the question). For the record, I would never tell my wife who she could or could not have at her defense. I'm just trying to be helpful :) It's encouraging to hear from the comments that parent attendance at a defense is fairly common place, so it will probably be no big deal.
Open to the public means ... open to the public (presuming they can sit quietly in a room for 2 hours or however long your wife's defense is). 

Moreover, (edit though I thought I was clear), it's very common in the US for family including parents and spouses to attend PhD defenses.

My wife and parents came to my defense (philosophy PhD USA). As did a friend of ours who was a foreigner living in America with no connection to philosophy. A philosophy PhD defense at least at my institution is them drilling you with every objection and reason that they think you're wrong for two solid hours. 

While I assume a nutrition science PhD has a different format, I hope that neither the committee nor the person defending the dissertation has much time to look around and see who came and to think odd thoughts about the professionalism of the candidate based on who came to their defense.