  We show that the best fits of the MSSM constrained by a simple SO(10) SUSY
GUT are consistent with the present data on the muon anomalous magnetic moment.
The best fits assume rather large values of tan$\beta\approx 50$, and in our
analysis they are not {\em a priori} correlated in any way, directly or
indirectly, with the experimental limit on $a_\mu$. Regions in the SUSY
parameter space, which are currently ruled out because of too large
$a_\mu^{SUSY}$, are already excluded in the global fit by excessive corrections
to $m_b$, unacceptable $BR(b\to s\gamma)$, or direct experimental limits on
sparticle masses. However, our results indicate that the accuracy expected in
the ongoing E821 experiment at BNL will eventually turn the muon anomalous
magnetic moment into a major constraint for this regime of the MSSM.
