If you are talking about the week immediately following Christmas and running into New Year's Day, the crowds will be some of the biggest of the year. We have been to WDW at all times of the year, and this wins "biggest crowds" hands down. However, if you know that going in and make your plans accordingly, it is a beautiful time of year to visit. All the decorations in the parks and hotels help extend the Christmas spirit for a few more days. We loved our Christmas visit, but having said that, it's one of those been there, done that kind of things for us. We probably wouldn't do it again because of the crowds.