Electron density enhancements in the topside ionosphere beneath the magnetospheric cusp are consistently observed under an optimum set of geophysical conditions. Average results deduced from Isis 2 topside sounder data show that the cusp-related electron density enhancements maximize at ~77.5¿ corrected geomagnetic latitude in midwinter near local noon during very quiet magnetospheric conditions. The magnitudes of the enhancements determined at nine topside heights range from a factor of ~2 at hmax to ~16 at 1400 km. Enhancements as large as these require in situ production at the peak and above, coupled to upward expansion due to the higher plasma temperatures found beneath the cusp. The observed large enhancements further indicate that the ionospheric plasma resides beneath the cusp precipitation long enough (at least a few tens of minutes) for substantial quantities of additional ionization to accumulate. During disturbed periods and in seasons other than midwinter the cusp signature in topside electron densities is, in general, much less well defined or altogether absent.