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.
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