First, you might take a look at

http://cpearson.com/excel/duplicat.htm

for other ways to deal with duplicates.

Autofilter will only show the first 1000 entries in the dropdown. See

http://contextures.com/xlautofilter02.html#Limits

for a workaround

In article ,
Minitman wrote:

I have a list that has over 3800 names in it. I am trying to use Auto
Filter to go though the list an remove duplicate entries (The list
started out with a little over 16000 entries and I am now down to a
little over 3800). I have to find duplicates and get the last date
and copy it next to the first date then delete all but the first date.
I was using the Auto Filter but ran into a wall! It only shows
everything up to M's and nothing after that.

Is there a way to show all of the list?