Did you ever go on vacation and have 100's of reminders fire when you return and open Outlook? While it's not as much of a problem with Outlook 2002/2003's unified reminder window, where you can select several items to dismiss or Dismiss All at once, dismissing reminders one at a time in older versions gets old fast.
In Outlook 2007 and older, go to Tools, Options, Other tab, Advanced button and remove the check to display the reminder. This has the same effect as dismissing reminders and will affect all past due reminders as well as any that come due while it's disabled.
In Outlook 2010 and 2013, reminders can be turned off in File, Options, Advanced.
When you return from vacation, don't forget to turn Reminders back on.
If you forgot to make the change and have 100's of reminders fire, you can turn off reminders, close then reopen Outlook. All past due reminders will be turned off (dismissed) for you when Outlook reopens.
Published November 30, 2004. Last updated on December 17, 2012.