  We analyze the possible magnitude of the supersymmetric contribution to
$g_\mu - 2$ in a flipped SU(5) GUT model. Unlike other GUT models which are
severely constrained by universality relations, in flipped SU(5) the U(1)
gaugino mass and the soft supersymmetry-breaking masses of right-handed
sleptons are unrelated to the other gaugino, slepton and squark masses.
Consequently, the lightest neutralino and the right-handed smuon may be light
enough to mitigate the discrepancy between the experimental measurement of
$g_\mu - 2$ and the Standard Model calculation, in which case they may be
detectable at the LHC and/or a 250 GeV $e^+ e^-$ collider, whereas the other
gauginos and sfermions are heavy enough to escape detection at the LHC.
