Mark
Just to clarify.
Custom Lists are not used in the manner you describe. See Bob's answer for
how to do the Data Validation list.
Custom Lists are used to create a list of data in adjacent cells as you
drag/copy down or across.
Example.....the days of the week are a Custom List, the alphabet is a custom
list.
George, Gord, Bob, Mark, Bill, John can be a custom list you add through
Tools>Options>Custom List.
Enter George in A1 then drag/copy down to get the other names in the list
entered in cells below.
There is a third "list type" which is "pick from list".
If you have data in a column or row and you right-click on a cell in that
column and select "pick from list" you will get a list of unique items to pick
from based on the data in the column.
Gord Dibben Excel MVP