Maybe they aren't real Excel dates, but text. You can check with the ISTEXT() function.
If they a

=DATE(RIGHT(A1,2)+2000,LEFT(A1,2),MID(A1,4,2))
and format as required

--
Kind regards,

Niek Otten
Microsoft MVP - Excel

"Greenback" wrote in message ...
|I have a spreadsheet sent to me and it has a column of dates in the following
| format - mm/dd/yy
| I would like to change them to yyyy/dd/mm but I can't seem to change
| existing format. Any ideas on how this is done?