You can do this with programming. There's a sample file he

http://www.contextures.com/excelfiles.html

Under Data Validation, look for 'Select Multiple Items from Dropdown List'

JMW wrote:
How do I allow users to select multiple options in a drop down list in Excel?
My drop dow list contains: RED, BLUE, GREEN, YELLOW
and users need to select 1-3 of the color selections.

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Debra Dalgleish
Excel FAQ, Tips & Book List
http://www.contextures.com/tiptech.html