Ion density measurements from the Dynamics Explorer 2 and Defense Meteorological Satellite Program F8 and F9 satellites are used to examine hemispherical differences in the occurrence patterns of polar ionization patches as a function of season, universal time (UT), and interplanetary magnetic field (IMF). When Bz<0, the greatest frequency of patch occurrence in the northern hemisphere is in the winter in the 1000--2200 UT range. This time corresponds to the interval when the northern magnetic pole (and hence the cusp) lies the farthermost toward the dayside. This fact is often used to explain the creation of patches in terms of the entrainment of dayside plasma into the cusp by high-latitude convection. In the southern hemisphere we see that the occurrence frequencies peak at over twice the northern hemisphere values in the same general UT region (1000--2300 UT). However, the southern hemisphere cusp is most dayward at approximately 0300 UT, a time of minimum patch formation. Examination of the relationship of the terminator to the polar cap boundaries in each hemisphere leads to a simple explanation in terms of the differing offset of the magnetic poles (and the ionospheric convection pattern) from the geographic poles. ¿ 1998 American Geophysical Union