I also think your feelings have to do with the idea of a vasectomy being so final. With the IUD, as you said, in the back of your mind there was always the possibility of having another child. Whereas with the vasectomy, there are no more chances to have a child. My husband and I agreed to have one child. Yet after she was born, I just couldn't bring myself to give away the maternity clothes! There's something so final about that. Even though I knew that I was comfortable with the decision to have just one child and would sometimes have dreams where I was pregnant again and very worried about it ("what are we going to do?", etc.). Yet I hung on to those maternity clothes for years. I finally gave them away when we knew there was no way another baby could come along due to my age! So--don't worry. In your head, you know that this decision is right for your family. And as far as the future goes, you can't fret over all the "what ifs". After all, who knows what will happen?