Depending on your Outlook version (which you decided was not important) there are several methods. The easiest is the one posted he http://www.slipstick.com/outlook/mru.htm

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Milly Staples [MVP - Outlook]

Post all replies to the group to keep the discussion intact.

After furious head scratching, Karole asked:

| How do I remove a colleagues calendar if no longer employed at work?
| I know how to add other calendars and share them etc but I have
| several old ones I wish to remove