In 2008, the American Community Survey (ACS)  changed the way it asks about disability.   Superficially, the differences between the 2007 questions and the 2008 questions may seem  unremarkable, however there are critical distinctions between the conceptual frameworks encompassing the two question sets. This paper describes some of these distinctions and demonstrates that the 2008 questions should not be used to make comparisons to earlier ACS disability estimates.