  The $^{174}$Yb($^{29}$Si,5n) reaction at 148 MeV with thin targets was used
to populate high-angular momentum states in $^{198}$Po. Resulting $\gamma$ rays
were observed with Gammasphere. A weakly-populated superdeformed band of 10
$\gamma$-ray transitions was found and has been assigned to $^{198}$Po. This is
the first observation of a SD band in the $A \approx 190$ region in a nucleus
with $Z > 83$. The ${\cal J}^{(2)}$ of the new band is very similar to those of
the yrast SD bands in $^{194}$Hg and $^{196}$Pb. The intensity profile suggests
that this band is populated through states close to where the SD band crosses
the yrast line and the angular momentum at which the fission process dominates.
