Should turkey be stuffed?

It isn't advisable, nor is the purchase of "pre-stuffed" turkey. The concern is that uncooked ingredients such as egg, mushroom, or onion may contain salmonella or other bacteria that can multiply quickly at temperatures of 40°F-140° F. Also, an over-stuffed bird may result in undercooked meat.
 
Traditionalists wishing to brave it should ensure both turkey and stuffing are cooked to an internal temperature of 165° F. Avoid overstuffing the bird, as it prolongs cooking times and can result in an undercooked turkey. Allow stuffing to cool down prior to inserting it in the raw turkey. Hot or warm stuffing can quickly promote bacterial growth in the raw carcass.
 
Sources:
USDA Fact Sheet "Turkey Basics: Stuffing"