Originally Posted by
philemer
From nwa.com: Please note: WorldPerks miles have no expiration date. However, consistent with the general terms and conditions of the WorldPerks program, Northwest Airlines reserves the right to change the WorldPerks program at any time without notice, including imposition of expiration limits or reactivation fees. If no mileage from any source is posted to a WorldPerks member’s account for three consecutive years, the account is subject to termination, including forfeiture of all accrued mileage..
Don't know of anyone that has ever lost any NW miles. That quote gives them the option, it does not require it.
Three years is still twice as long as 18 months even if they did take them, most other programs have gone to 18 month expirations.