I always had an aversion to calling my wife's mother Mom. It just didn't seem right to me. I have one mother, my Mom. I just couldn't call my wife's mother Mom. I felt funny about it. I kind of felt bad and it wasn't meant to diminish my love and respect for her but she isn't my Mom. I wouldn't even consider calling her by her first name either. You can go years and years and years without ever being in a position where you would need to make a choice. Do all of you call your mother in law Mom ?