  We compute low temperature corrections to the electromagnetic mass difference
of pions in the chiral limit. The computation is done in a model independent
way in the framework of chiral perturbation theory, using the background field
method and the hard thermal loop approximation. We also generalize at low
temperature the sum rule of Das et al. We find that the mass difference between
the charged and neutral pions decreases at low temperature $T$ with respect to
the T=0 value. This is so in spite of the fact that charged particles always
get a thermal correction to their masses of order $\sim eT$, where $e$ is the
gauge coupling constant. Our result can be understood as a consequence of the
tendency towards chiral symmetry restoration at finite temperature.
