According to an aspect of the invention, injectable bulking compositions are provided which contain the following: (a) fibers that are configured to prevent migration to locations in the body remote from the injection site, for example, because they have a minimum length that is sufficiently large to prevent migration of the fibers and/or because they have surface features that stimulate host tissue response to lock the fibers in position and (b) a carrier in an amount effective to render the composition injectable.
