  Demagnetization, which is inherently present in the magnetic response of
small finite-size superconductors, can be accounted for by an effective
$\kappa$ within a two-dimensional lowest Landau level approximation of the
Ginzburg-Landau functional. We show this by comparing the equilibrium
magnetization of superconducting mesoscopic disks obtained from the numerical
solution of the three-dimensional Ginzburg-Landau equations with that obtained
in the ``effective'' LLL approximation.
