We study the linearized stability of n-vortex (n is an element of Z) soluti
ons of the magnetic Ginzburg-Landau (or Abelian Higgs) equations. We prove
that the fundamental vortices (n = +/-1) are stable for all values of the c
oupling constant, lambda, and we prove that the higher-degree vortices (\ n
\ greater than or equal to 2) are stable for lambda < 1, and unstable for
lambda > 1. This resolves a long-standing conjecture (see, eg, [JT]).