  In simple SO(10) SUSY GUTs the top, bottom and tau Yukawa couplings unify at
the GUT scale. A naive renormalization group analysis, neglecting weak scale
threshold corrections, leads to moderate agreement with the low energy data.
However it is known that intrinsically large threshold corrections proportional
to $\tan\beta \sim m_t(M_Z)/m_b(M_Z) \sim 50$ can nullify these $t, b$, $\tau$
mass predictions. In this paper we turn the argument around. Instead of
predicting fermion masses, we use the constraint of Yukawa unification and the
observed values $M_t, m_b(m_b), M_\tau$ to constrain SUSY parameter space. We
find a narrow region survives for $\mu > 0$ with $\mu, M_{1/2} << m_{16}$, $A_0
\approx - 1.9 m_{16}$ and $m_{16} > 1200$ \gev. Demanding Yukawa unification
thus makes definite predictions for Higgs and sparticle masses. In particular
we find a light higgs with mass $m_h^0 = 114 \pm 5 \pm 3$ GeV and a light stop
with $(m_{\tilde t_1})_{MIN} \sim 450$ GeV and $m_{\tilde t_1} << m_{\tilde
b_1}$. In addition, we find a light chargino and a neutralino LSP. It is also
significant that in this region of parameter space the SUSY contribution to the
muon anomalous magnetic moment $a_\mu^{SUSY} < 16 \times 10^{-10}$.
